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Coding Style

Hung-Wei Liu, profile picture
Hung-Wei Liu

The document discusses techniques for organizing code structures like straight line code and conditionals to improve readability and maintainability. It covers organizing straight line code by making dependencies obvious, keeping related statements together, and grouping related blocks. For conditionals, it recommends writing nominal cases first, simplifying complex tests, putting common cases first, and ensuring all cases are covered.

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Overview . . . . . . . . . . . Organizing Straight Line Code . . . . . . . . . . . Using Conditionals . . . . . . Unusual Control Structures Taming Deep Nesting Code Complete Series Aecho Penpower, Inc aecho.liu@penpower.com.tw 2013, 06 1 / 50
Overview . . . . . . . . . . . Organizing Straight Line Code . . . . . . . . . . . Using Conditionals . . . . . . Unusual Control Structures Taming Deep Nesting Overview Overview Organizing Straight Line Code With Specific order Statements whose order doesn’t matter Using Conditionals If statements Case statements Unusual Control Structures Multiple returns from a routine gotos Taming Deep Nesting 2 / 50
Overview . . . . . . . . . . . Organizing Straight Line Code . . . . . . . . . . . Using Conditionals . . . . . . Unusual Control Structures Taming Deep Nesting References Code Complete 2ed • Ch 14, Organizing Straight Line Code • Ch 15, Using Conditionals • Ch 17, Unusual Control Structures • Ch 19.4, Taming Deep Nesting 3 / 50
Overview . . . . . . . . . . . Organizing Straight Line Code . . . . . . . . . . . Using Conditionals . . . . . . Unusual Control Structures Taming Deep Nesting Overview Improve code qualities • Readability • Maintainability 4 / 50
Overview . . . . . . . . . . . Organizing Straight Line Code . . . . . . . . . . . Using Conditionals . . . . . . Unusual Control Structures Taming Deep Nesting Organizing Straight Line Code Statement order can be one of following categories • must be a specific order • order doesn’t matter . Sample of straight line codes .. ...... Foo () ; HelloWorld () ; f o r ( i n t i = 0; i < 100; i ++) { H e l l o K i t t y ( ) ; } 5 / 50
Overview . . . . . . . . . . . Organizing Straight Line Code . . . . . . . . . . . Using Conditionals . . . . . . Unusual Control Structures Taming Deep Nesting With specific order . Run with specific order. The dependencies are obvious. .. ...... data = ReadData(); result = GetResultsFromData(data); PrintResults(results); 6 / 50
Overview . . . . . . . . . . . Organizing Straight Line Code . . . . . . . . . . . Using Conditionals . . . . . . Unusual Control Structures Taming Deep Nesting With specific order . Run with specific order. The dependencies are not obvious. .. ...... revenue.ComputeMonthly(); revenue.ComputeQuarterly(); revenue.ComputeAnnual(); 7 / 50
Overview . . . . . . . . . . . Organizing Straight Line Code . . . . . . . . . . . Using Conditionals . . . . . . Unusual Control Structures Taming Deep Nesting With specific order Make the dependences obvious. • Organize code • Name routine • Use routine parameters • Document dependencies with comments • Check dependencies with assertions or error-handling 8 / 50
Overview . . . . . . . . . . . Organizing Straight Line Code . . . . . . . . . . . Using Conditionals . . . . . . Unusual Control Structures Taming Deep Nesting With specific order . With specific order, but not obviously. .. ...... ComputeMarketingExpense () ComputeSalesExpense () ComputeTravelExpense () ComputePersonnelExpense () DisplayExpenseSummary () • The ComputeMarketingExpense() will initialize the expense. • The dependencies are not obvious in above codes. 9 / 50
Overview . . . . . . . . . . . Organizing Straight Line Code . . . . . . . . . . . Using Conditionals . . . . . . Unusual Control Structures Taming Deep Nesting With specific order • The parameter expense gives a hint the following routines are grouped. • The names of InitialExpenseData() and DisplayExpenseSummary() are obvious executed at first and last. . Grouped with routine parameter .. ...... I n i t i a l E x p e n s e D a t a ( expense ) ; ComputeMarketingExpense ( expense ) ; ComputeSalesExpense ( expense ) ; ComputeTravelExpense ( expense ) ; ComputePersonalExpense ( expense ) ; DisplayExpenseSummary ( expense ) ; 10 / 50
Overview . . . . . . . . . . . Organizing Straight Line Code . . . . . . . . . . . Using Conditionals . . . . . . Unusual Control Structures Taming Deep Nesting With specific order . Document dependencies with comments .. ...... /∗∗ ∗ Compute expense data . Each of the r o u t i n e s a c c e s s e s ∗ the member data expenseData . DisplayExpenseSummary ∗ should be c a l l e d l a s t because i t depends on data ∗ c a l c u l a t e d by the other r o u t i n e s . ∗/ I n i t i a l E x p e n s e D a t a ( expense ) ; ComputeMarketingExpense ( expense ) ; ComputeSalesExpense ( expense ) ; ComputeTravelExpense ( expense ) ; ComputePersonalExpense ( expense ) ; DisplayExpenseSummary ( expense ) ; 11 / 50
Overview . . . . . . . . . . . Organizing Straight Line Code . . . . . . . . . . . Using Conditionals . . . . . . Unusual Control Structures Taming Deep Nesting Statements whose order doesn’t matter • In the absence of routine dependencies, we can order statement or block of code ... • Keep related actions together. • Grouping related statements. • Ordering affects the readability, performance, maintainability. 12 / 50
Overview . . . . . . . . . . . Organizing Straight Line Code . . . . . . . . . . . Using Conditionals . . . . . . Unusual Control Structures Taming Deep Nesting Keep related actions together . The related actions are not together, but jump around .. ...... MarketingData marketingData ; SalesData s a l e s D a t a ; TravelData t r a v e l D a t a ; t r a v e l D a t a . ComputeQuarterly () ; s a l e s D a t a . ComputeQuarterly () ; marketingData . ComputeQuarterly () ; s a l e s D a t a . ComputeAnnual () ; marketingData . ComputeAnnual () ; t r a v e l D a t a . ComputeAnnual () ; s a l e s D a t a . P r i n t () ; t r a v e l D a t a . P r i n t () ; marketingData . P r i n t () ; 13 / 50
Overview . . . . . . . . . . . Organizing Straight Line Code . . . . . . . . . . . Using Conditionals . . . . . . Unusual Control Structures Taming Deep Nesting Keep related actions together . The related actions are together .. ...... MarketingData marketingData ; marketingData . ComputeQuarterly () ; marketingData . ComputeAnnual () ; marketingData . P r i n t () ; SalesData s a l e s D a t a ; s a l e s D a t a . ComputeQuarterly () ; s a l e s D a t a . ComputeAnnual () ; s a l e s D a t a . P r i n t () ; TravelData t r a v e l D a t a ; t r a v e l D a t a . ComputeQuarterly () ; t r a v e l D a t a . ComputeAnnual () ; t r a v e l D a t a . P r i n t () ; 14 / 50
Overview . . . . . . . . . . . Organizing Straight Line Code . . . . . . . . . . . Using Conditionals . . . . . . Unusual Control Structures Taming Deep Nesting Grouping related statements 15 / 50
Overview . . . . . . . . . . . Organizing Straight Line Code . . . . . . . . . . . Using Conditionals . . . . . . Unusual Control Structures Taming Deep Nesting Grouping related statements Bad grouped statements 16 / 50
Overview . . . . . . . . . . . Organizing Straight Line Code . . . . . . . . . . . Using Conditionals . . . . . . Unusual Control Structures Taming Deep Nesting Grouping related statements Bad grouped statements Well grouped statements 17 / 50
Overview . . . . . . . . . . . Organizing Straight Line Code . . . . . . . . . . . Using Conditionals . . . . . . Unusual Control Structures Taming Deep Nesting Key points • The strongest principle for organizing straight-line code is ordering dependencies. • Dependencies should be made obvious through the use of good routine names, parameter lists, comments. • If code doesn’t have order dependencies, keep related statements as close together as possible. 18 / 50
Overview . . . . . . . . . . . Organizing Straight Line Code . . . . . . . . . . . Using Conditionals . . . . . . Unusual Control Structures Taming Deep Nesting Using Conditionals Using Conditionals: • if statements • case statements 19 / 50
Overview . . . . . . . . . . . Organizing Straight Line Code . . . . . . . . . . . Using Conditionals . . . . . . Unusual Control Structures Taming Deep Nesting If statements Guidelines for If statements • Write the nominal path through the code first; then write the unusual cases. • Simplify complicated cases with boolean function calls. • Put the common cases first. • Make sure all cases are covered. 20 / 50
Overview . . . . . . . . . . . Organizing Straight Line Code . . . . . . . . . . . Using Conditionals . . . . . . Unusual Control Structures Taming Deep Nesting If statements Write the nominal path through the code first; then write the unusual cases. . OpenFile ( i n p u t F i l e , s t a t u s ) ; i f ( s t a t u s == S t a t u s E r r o r ) { errorType = Fil eOpe nError ; // 1 , E r r o r Case } e l s e { ReadFile ( i n p u t F i l e , f i l e D a t a , s t a t u s ) ; // 2 , Normal Case i f ( s t a t u s == S t a t u s S u c c e s s ) { SummarizeFileData ( f i l e D a t a , summaryData , s t a t u s ) ; // 3 , Normal Case i f ( s t a t u s == S t a t u s E r r o r ) { errorType = ErrorTypeDataSummaryError ; // 4 , E r r o r Case } e l s e { PrintSummary ( summaryData ) ; // 5 , Normal case SaveSummaryData ( summaryData , s t a t u s ) ; i f ( s t a t u s == S t a t u s E r r o r ) { errorType = SummarySaveError ; // 6 , E r r o r case } e l s e { UpdateAllCounts () ; // 7 , Normal case EraseUndoFiles ( ) ; errorType = ErrorTypeNone ; } } } e l s e { errorType = F i l e R e a d E r r o r ; // } } 21 / 50
Overview . . . . . . . . . . . Organizing Straight Line Code . . . . . . . . . . . Using Conditionals . . . . . . Unusual Control Structures Taming Deep Nesting If statements Write the nominal path through the code first; then write the unusual cases. . OpenFile ( i n p u t F i l e , s t a t u s ) ; i f ( s t a t u s == Status Suc cess ) { ReadFile ( i n p u t F i l e , f i l e D a t a , s t a t u s ) ; // 1 , Normal Case i f ( s t a t u s == S t a t u s S u c c e s s ) { SummarizeFileData ( f i l e D a t a , summaryData , s t a t u s ) ; // 2 , Normal Case i f ( s t a t u s == S t a t u s S u c c e s s ) { PrintSummary ( summaryData ) ; // 3 , Normal case SaveSummaryData ( summaryData , s t a t u s ) ; i f ( s t a t u s == StatusSuccess ) { UpdateAllCounts () ; // 4 , Normal case EraseUndoFiles ( ) ; errorType = ErrorTypeNone ; } e l s e { errorType = SummarySaveError ; // 5 , E r r o r case } } e l s e { errorType = ErrorTypeDataSummaryError ; // 6 , E r r o r Case } } e l s e { errorType = F i l e R e a d E r r o r ; // 7 , E r r o r Case } } e l s e { errorType = Fil eOpe nError ; // } 22 / 50
Overview . . . . . . . . . . . Organizing Straight Line Code . . . . . . . . . . . Using Conditionals . . . . . . Unusual Control Structures Taming Deep Nesting If statements 1. Error Case 2. Normal Case 3. Normal Case 4. Error Case 5. Normal Case 6. Error Case 7. Normal Case 1. Normal Case 2. Normal Case 3. Normal Case 4. Normal Case 5. Error Case 6. Error Case 7. Error Case Easier to find the normal path through the codes. 23 / 50
Overview . . . . . . . . . . . Organizing Straight Line Code . . . . . . . . . . . Using Conditionals . . . . . . Unusual Control Structures Taming Deep Nesting If statements Simplify complicated tests with boolean function calls . i f ( i n p u t C h a r a c t e r < SPACE ) { characterType = CharacterType ControlCharacter ; } e l s e i f ( i n p u t C h a r a c t e r == ’ ’ | | i n p u t C h a r a c t e r == ’ , ’ | | i n p u t C h a r a c t e r == ’ . ’ | | i n p u t C h a r a c t e r == ’ ! ’ | | i n p u t C h a r a c t e r == ’ ( ’ | | i n p u t C h a r a c t e r == ’ ) ’ | | i n p u t C h a r a c t e r == ’ : ’ | | i n p u t C h a r a c t e r == ’ ; ’ | | i n p u t C h a r a c t e r == ’ ? ’ | | i n p u t C h a r a c t e r == ’−’ ){ characterType = CharacterType Punctuation ; } e l s e i f ( ’ 0 ’ <= i n p u t C h a r a c t e r && i n p u t C h a r a c t e r <= ’ 9 ’ ) { characterType = C har a cterTyp e Dig it ; } e l s e i f ( ( ’ a ’ <= i n p u t C h a r a c t e r && i n p u t C h a r a c t e r <= ’ z ’ ) | | ( ’A ’ <= i n p u t C h a r a c t e r && i n p u t C h a r a c t e r <= ’Z ’ ) ) { characterType = C h a r a c t e r T y p e Le t t e r ; } 24 / 50
Overview . . . . . . . . . . . Organizing Straight Line Code . . . . . . . . . . . Using Conditionals . . . . . . Unusual Control Structures Taming Deep Nesting If statements Simplify complicated tests with boolean function calls . With boolean function calls .. ...... i f ( I s C o n t r o l ( i n p u t C h a r a c t e r ) ) { characterType = CharacterType ControlCharacter ; } e l s e i f ( I s P u n c t u a t i o n ( i n p u t C h a r a c t e r ) ) { characterType = CharacterType Punctuation ; } e l s e i f ( I s D i g i t ( i n p u t C h a r a c t e r ) ) { characterType = C har a cterTyp e Dig it ; } e l s e i f ( I s L e t t e r ( i n p u t C h a r a c t e r ) ) { characterType = C h a r a c t e r T y p e Le t t e r ; } 25 / 50
Overview . . . . . . . . . . . Organizing Straight Line Code . . . . . . . . . . . Using Conditionals . . . . . . Unusual Control Structures Taming Deep Nesting If statements Put the most common cases first. . Most common case first .. ...... i f ( I s L e t t e r ( i n p u t C h a r a c t e r ) ) { // The most common case characterType = C h a r a c t e r T y p e Le t t e r ; } e l s e i f ( I s P u n c t u a t i o n ( i n p u t C h a r a c t e r ) ) { characterType = CharacterType Punctuation ; } e l s e i f ( I s D i g i t ( i n p u t C h a r a c t e r ) ) { characterType = C har a cterTyp e Dig it ; } e l s e i f ( I s C o n t r o l ( i n p u t C h a r a c t e r ) ) { // The l e a s t common case characterType = CharacterType ControlCharacter ; } 26 / 50
Overview . . . . . . . . . . . Organizing Straight Line Code . . . . . . . . . . . Using Conditionals . . . . . . Unusual Control Structures Taming Deep Nesting If statements Use default case to trap errors. . Trap the errors with default case. .. ...... i f ( I s L e t t e r ( i n p u t C h a r a c t e r ) ) { characterType = C h a r a c t e r T y p e Le t t e r ; } e l s e i f ( I s P u n c t u a t i o n ( i n p u t C h a r a c t e r ) ) { characterType = CharacterType Punctuation ; } e l s e i f ( I s D i g i t ( i n p u t C h a r a c t e r ) ) { characterType = C har a cterTyp e Dig it ; } e l s e i f ( I s C o n t r o l ( i n p u t C h a r a c t e r ) ) { characterType = CharacterType ControlCharacter ; } e l s e { // Trap the e r r o r s . D i s p l a y I n t e r n a l E r r o r ( ” Unexpected type of c h a r a c t e r detected . ” ) ; } 27 / 50
Overview . . . . . . . . . . . Organizing Straight Line Code . . . . . . . . . . . Using Conditionals . . . . . . Unusual Control Structures Taming Deep Nesting Case Statements Choosing the Most Effective Ordering of Cases • Order cases alphabetically or numerically If cases are equally important, putting them in A-B-C order to improves readability. • Put the normal case first • Order cases by frequency Put the most frequently executed cases first and the least frequently executed last. • Human readers can find the most common cases easily. • Putting the common ones at the top of the code makes the search quicker. 28 / 50
Overview . . . . . . . . . . . Organizing Straight Line Code . . . . . . . . . . . Using Conditionals . . . . . . Unusual Control Structures Taming Deep Nesting Case statements Tips of using case statements • Keep the actions of each case simple. Extract complicated codes to routine. • Use the default clause to detect errors. 29 / 50
Overview . . . . . . . . . . . Organizing Straight Line Code . . . . . . . . . . . Using Conditionals . . . . . . Unusual Control Structures Taming Deep Nesting Case statements Tips of using case statements • Keep the actions of each case simple. Extract complicated codes to routine. • Use the default clause to detect errors. . ...... switch ( commandShortcutLetter ) { case ’ a ’ : PrintAnnualReport () ; break ; case ’ p ’ : // no a c t i o n r e q u i r e d , but case was c o n s i d e r e d break ; case ’ q ’ : P r i n t Q u a r t e r l y R e p o r t () ; break ; case ’ s ’ : PrintSummaryReport () ; break ; d e f a u l t : // Detect e r r o r s . D i s p l a y I n t e r n a l E r r o r ( ” I n t e r n a l E r r o r 905: C a l l customer support . ” ) ; } 30 / 50
Overview . . . . . . . . . . . Organizing Straight Line Code . . . . . . . . . . . Using Conditionals . . . . . . Unusual Control Structures Taming Deep Nesting Case statements • Generally, code that falls through one case to another is an invitation to make mistake as the code is modified. It should be avoided. • Clearly and unmistakably identify the flow-through at the end of case statement. . ...... switch ( errorDocumentationLevel ) { case DocumentationLevel Full : D i s p l a y E r r o r D e t a i l s ( errorNumber ) ; // FALLTHROUGH −− F u l l documentation a l s o p r i n t s summary comments case DocumentationLevel Summary : DisplayErrorSummary ( errorNumber ) ; // FALLTHROUGH −− Summary documentation a l s o p r i n t s e r r o r number case DocumentationLevel NumberOnly : DisplayErrorNumber ( errorNumber ) ; break ; d e f a u l t : D i s p l a y I n t e r n a l E r r o r ( ” I n t e r n a l E r r o r 905: C a l l customer support . ” ) ; } 31 / 50
Overview . . . . . . . . . . . Organizing Straight Line Code . . . . . . . . . . . Using Conditionals . . . . . . Unusual Control Structures Taming Deep Nesting Unusual Control Structure • Multiple returns from a routine • goto 32 / 50
Overview . . . . . . . . . . . Organizing Straight Line Code . . . . . . . . . . . Using Conditionals . . . . . . Unusual Control Structures Taming Deep Nesting Multiple returns from a routine Multiple returns from a routine. • Use a return when it enhances readability. • Use guard clauses1 to simplify the complex error processing. 1 Check invalid conditions and return error code directly. 33 / 50
Overview . . . . . . . . . . . Organizing Straight Line Code . . . . . . . . . . . Using Conditionals . . . . . . Unusual Control Structures Taming Deep Nesting Multiple returns from a routine . Multiple returns from a routine .. ...... Comparison Compare ( i n t value1 , i n t value2 ) { i f ( value1 < value2 ) { r e t u r n Comparison LessThan ; } e l s e i f ( value1 > value2 ) { r e t u r n Comparison GreaterThan ; } r e t u r n Comparison Equal ; } 34 / 50
Overview . . . . . . . . . . . Organizing Straight Line Code . . . . . . . . . . . Using Conditionals . . . . . . Unusual Control Structures Taming Deep Nesting Multiple returns from a routine This codes can be re written with multiple returns... . Deep nesting .. ...... i f ( f i l e . validName () ) { i f ( f i l e . Open () ) { i f ( encryptionKey . v a l i d () ) { i f ( f i l e . Decrypt ( encryptionKey ) { // l o t s of statements // . . . } } } } 35 / 50
Overview . . . . . . . . . . . Organizing Straight Line Code . . . . . . . . . . . Using Conditionals . . . . . . Unusual Control Structures Taming Deep Nesting Multiple returns from a routine . Use guard clauses to clarify the nominal cases .. ...... i f ( ! f i l e . validName () ) r e t u r n ; i f ( ! f i l e . open () ) r e t u r n ; i f ( ! encryptionKey . v a l i d () ) r e t u r n ; i f ( ! f i l e . Decrypt ( encryptionKey ) ) r e t u r n ; // l o t s of statements // . . . 36 / 50
Overview . . . . . . . . . . . Organizing Straight Line Code . . . . . . . . . . . Using Conditionals . . . . . . Unusual Control Structures Taming Deep Nesting Multiple returns from a routine . More realistic codes. Use guard clauses to clarify the nominal cases .. ...... i f ( ! f i l e . validName () ) r e t u r n F i l e E r r o r I n v a l i d N a m e ; i f ( ! f i l e . open () ) r e t u r n F i l e E r r o r C a n t O p e n F i l e ; i f ( ! encryptionKey . v a l i d () ) r e t u r n F i l e E r r o r I n v a l i d E n c r y p t i o n K e y ; i f ( ! f i l e . Decrypt ( encryptionKey ) ) r e t u r n F i l e E r r o r C a n t D e c r y p t F i l e ; // l o t s of statements // . . . 37 / 50
Overview . . . . . . . . . . . Organizing Straight Line Code . . . . . . . . . . . Using Conditionals . . . . . . Unusual Control Structures Taming Deep Nesting gotos About goto statements. • Generally, Without goto → High quality codes • Under some situations, goto → High readability and maintainability. 38 / 50
Overview . . . . . . . . . . . Organizing Straight Line Code . . . . . . . . . . . Using Conditionals . . . . . . Unusual Control Structures Taming Deep Nesting gotos . Error processing and gotos .. e r r o r S t a t e = F i l e S t a t u s S u c c e s s ; f i l e I n d e x = 0; w h i l e ( f i l e I n d e x < numFilesToPurge ) { f i l e I n d e x += 1; i f ( ! F i n d F i l e ( f i l e L i s t ( f i l e I n d e x ) , f i l e T o P u r g e ) ) { e r r o r S t a t e = F i l e S t a t u s F i l e F i n d E r r o r ; goto End Proc ; } i f ( ! OpenFile ( f i l e T o P u r g e ) ) { e r r o r S t a t e = F i l e S t a t u s F i l e O p e n E r r o r ; goto End Proc ; } i f ( ! O v e r w r i t e F i l e ( f i l e T o P u r g e ) ) { e r r o r S t a t e = F i l e S t a t u s F i l e O v e r w r i t e E r r o r ; goto End Proc ; } i f ( ! Erase ( f i l e T o P u r g e ) ){ e r r o r S t a t e = F i l e S t a t u s F i l e E r a s e E r r o r ; goto End Proc ; } End Proc : D e l e t e P u r g e F i l e L i s t ( f i l e L i s t , numFilesToPurge ) ; 39 / 50
Overview . . . . . . . . . . . Organizing Straight Line Code . . . . . . . . . . . Using Conditionals . . . . . . Unusual Control Structures Taming Deep Nesting Taming Deep Nesting • Few people can understand more than 3 level of nested if. 1986, Noam Chomsky, and Gerald Weinberg. • Many researchers recommend avoiding nesting more than 3 or 4 levels. Myers 1976, Marca 1981, and Ledgard and Tauer 1987a. 40 / 50
Overview . . . . . . . . . . . Organizing Straight Line Code . . . . . . . . . . . Using Conditionals . . . . . . Unusual Control Structures Taming Deep Nesting Taming Deep Nesting . deep nesting if .. ...... i f ( i n p u t S t a t u s == I n p u t S t a t u s S u c c e s s ) { // l o t s of code . . . i f ( p r i n t e r R o u t i n e != NULL ) { // l o t s of code . . . i f ( SetupPage () ) { // l o t s of code . . . i f ( AllocMem ( &printData ) ) { // l o t s of code . . . } } } } 41 / 50
Overview . . . . . . . . . . . Organizing Straight Line Code . . . . . . . . . . . Using Conditionals . . . . . . Unusual Control Structures Taming Deep Nesting Taming Deep Nesting . Simplify a nested if by retesting part of the condition .. i f ( i n p u t S t a t u s != I n p u t S t a t u s S u c c e s s ) goto EXIT ; // l o t s of code . . . i f ( p r i n t e r R o u t i n e == NULL ) goto EXIT ; // l o t s of code . . . i f ( ! SetupPage () ) goto EXIT ; // l o t s of code . . . i f ( ! AllocMem ( &printData ) ) goto EXIT ; // l o t s of code . . . EXIT : r e t u r n ; 42 / 50
Overview . . . . . . . . . . . Organizing Straight Line Code . . . . . . . . . . . Using Conditionals . . . . . . Unusual Control Structures Taming Deep Nesting Taming Deep Nesting . Simplify a nested if by using a break block .. do { i f ( i n p u t S t a t u s != I n p u t S t a t u s S u c c e s s ) break ; // l o t s of code . . . i f ( p r i n t e r R o u t i n e == NULL ) break ; // l o t s of code . . . i f ( ! SetupPage () ) break ; // l o t s of code . . . i f ( ! AllocMem ( &printData ) ) break ; // l o t s of code . . . } w h i l e ( f a l s e ) ; 43 / 50
Overview . . . . . . . . . . . Organizing Straight Line Code . . . . . . . . . . . Using Conditionals . . . . . . Unusual Control Structures Taming Deep Nesting Taming Deep Nesting . Overgrown decision tree .. ...... i f ( 10 < q u a n t i t y ) { i f ( 100 < q u a n t i t y ) { i f ( 1000 < q u a n t i t y ) { d i s c o u n t = 0 . 1 0 ; } e l s e { d i s c o u n t = 0 . 0 5 ; } } e l s e { d i s c o u n t = 0 . 0 2 5 ; } } e l s e { d i s c o u n t = 0 . 0 ; } 44 / 50
Overview . . . . . . . . . . . Organizing Straight Line Code . . . . . . . . . . . Using Conditionals . . . . . . Unusual Control Structures Taming Deep Nesting Taming Deep Nesting . Convert to a set by if-then-elses .. ...... i f ( 1000 < q u a n t i t y ) { d i s c o u n t = 0 . 1 0 ; } e l s e i f ( 100 < q u a n t i t y ) { d i s c o u n t = 0 . 0 5 ; } e l s e i f ( 10 < q u a n t i t y ) { d i s c o u n t = 0 . 0 2 5 ; } e l s e { d i s c o u n t = 0; } 45 / 50
Overview . . . . . . . . . . . Organizing Straight Line Code . . . . . . . . . . . Using Conditionals . . . . . . Unusual Control Structures Taming Deep Nesting Taming Deep Nesting . Convert to a set by if-then-elses .. ...... i f ( 1000 < q u a n t i t y ) { d i s c o u n t = 0 . 1 0 ; } e l s e i f ( ( 100 < q u a n t i t y ) && ( q u a n t i t y <= 1000 ) ) { d i s c o u n t = 0 . 0 5 ; } e l s e i f ( ( 10 < q u a n t i t y ) && ( q u a n t i t y <= 100 ) ) { d i s c o u n t = 0 . 0 2 5 ; } e l s e i f ( q u a n t i t y <= 10 ) { d i s c o u n t = 0; } 46 / 50
Overview . . . . . . . . . . . Organizing Straight Line Code . . . . . . . . . . . Using Conditionals . . . . . . Unusual Control Structures Taming Deep Nesting Taming Deep Nesting . // p r o c e s s t r a n s a c t i o n depending on type of t r a n s a c t i o n i f ( t r a n s a c t i o n . Type == TransactionType Deposit ) { // p r o c e s s a d e p o s i t i f ( t r a n s a c t i o n . AccountType == AccountType Checking ) { i f ( t r a n s a c t i o n . AccountSubType == AccountSubType Business ) MakeBusinessCheckDep ( t r a n s a c t i o n . AccountNum , t r a n s a c t i o n . Amount ) ; e l s e i f ( t r a n s a c t i o n . AccountSubType == AccountSubType Personal ) MakePersonalCheckDep ( t r a n s a c t i o n . AccountNum , t r a n s a c t i o n . Amount ) ; e l s e i f ( t r a n s a c t i o n . AccountSubType == AccountSubType School ) MakeSchoolCheckDep ( t r a n s a c t i o n . AccountNum , t r a n s a c t i o n . Amount ) ; } e l s e i f ( t r a n s a c t i o n . AccountType == AccountType Savings ) MakeSavingsDep ( t r a n s a c t i o n . AccountNum , t r a n s a c t i o n . Amount ) ; e l s e i f ( t r a n s a c t i o n . AccountType == AccountType DebitCard ) MakeDebitCardDep ( t r a n s a c t i o n . AccountNum , t r a n s a c t i o n . Amount ) ; e l s e i f ( t r a n s a c t i o n . AccountType == AccountType MoneyMarket ) MakeMoneyMarketDep ( t r a n s a c t i o n . AccountNum , t r a n s a c t i o n . Amount ) ; e l s e i f ( t r a n s a c t i o n . AccountType == AccountType Cd ) MakeCDDep( t r a n s a c t i o n . AccountNum , t r a n s a c t i o n . Amount ) ; } e l s e i f ( t r a n s a c t i o n . Type == TransactionType Withdrawal ) { // p r o c e s s a withdrawal i f ( t r a n s a c t i o n . AccountType == AccountType Checking ) MakeCheckingWithdrawal ( t r a n s a c t i o n . AccountNum , t r a n s a c t i o n . Amount ) ; e l s e i f ( t r a n s a c t i o n . AccountType == AccountType Savings ) MakeSavingsWithdrawal ( t r a n s a c t i o n . AccountNum , t r a n s a c t i o n . Amount ) ; e l s e i f ( t r a n s a c t i o n . AccountType == AccountType DebitCard ) MakeDebitCardWithdrawal ( t r a n s a c t i o n . AccountNum , t r a n s a c t i o n . Amount ) ; } 47 / 50
Overview . . . . . . . . . . . Organizing Straight Line Code . . . . . . . . . . . Using Conditionals . . . . . . Unusual Control Structures Taming Deep Nesting Taming Deep Nesting . Factor deeply nested code into its routine .. // p r o c e s s t r a n s a c t i o n depending on type of t r a n s a c t i o n i f ( t r a n s a c t i o n . Type == TransactionType Deposit ) { ProcessDeposit ( t r a n s a c t i o n . AccountType , t r a n s a c t i o n . AccountSubType , t r a n s a c t i o n . AccountNum , t r a n s a c t i o n . Amount ) ; } e l s e i f ( t r a n s a c t i o n . Type == TransactionType Withdrawal ) { ProcessWithdrawal ( t r a n s a c t i o n . AccountType , t r a n s a c t i o n . AccountNum , t r a n s a c t i o n . Amount ) ; } e l s e i f ( t r a n s a c t i o n . Type == TransactionType Transfer ) { MakeFundsTransfer ( t r a n s a c t i o n . SourceAccountType , t r a n s a c t i o n . TargetAccountType , t r a n s a c t i o n . AccountNum , t r a n s a c t i o n . Amount ) ; } e l s e { // p r o c e s s unknown t r a n s a c t i o n type LogTransactionError ( ”Unknown Transaction Type” , t r a n s a c t i o n ) ; } 48 / 50
Overview . . . . . . . . . . . Organizing Straight Line Code . . . . . . . . . . . Using Conditionals . . . . . . Unusual Control Structures Taming Deep Nesting Taming Deep Nesting Summary of Techniques for Reducing Deep Nesting • Retest the part of condition. • Convert to if-then-elses. • Factor deeply nested code into its own routine. • Use objects and polymorphic dispatch. Design pattern. Ex, Strategy pattern, State pattern, ... etc. • ... etc. 49 / 50
Overview . . . . . . . . . . . Organizing Straight Line Code . . . . . . . . . . . Using Conditionals . . . . . . Unusual Control Structures Taming Deep Nesting Ending Any questions ? 50 / 50

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Coding Style

  • 1. Overview . . . . . . . . . . . Organizing Straight Line Code . . . . . . . . . . . Using Conditionals . . . . . . Unusual Control Structures Taming Deep Nesting Code Complete Series Aecho Penpower, Inc [email protected] 2013, 06 1 / 50
  • 2. Overview . . . . . . . . . . . Organizing Straight Line Code . . . . . . . . . . . Using Conditionals . . . . . . Unusual Control Structures Taming Deep Nesting Overview Overview Organizing Straight Line Code With Specific order Statements whose order doesn’t matter Using Conditionals If statements Case statements Unusual Control Structures Multiple returns from a routine gotos Taming Deep Nesting 2 / 50
  • 3. Overview . . . . . . . . . . . Organizing Straight Line Code . . . . . . . . . . . Using Conditionals . . . . . . Unusual Control Structures Taming Deep Nesting References Code Complete 2ed • Ch 14, Organizing Straight Line Code • Ch 15, Using Conditionals • Ch 17, Unusual Control Structures • Ch 19.4, Taming Deep Nesting 3 / 50
  • 4. Overview . . . . . . . . . . . Organizing Straight Line Code . . . . . . . . . . . Using Conditionals . . . . . . Unusual Control Structures Taming Deep Nesting Overview Improve code qualities • Readability • Maintainability 4 / 50
  • 5. Overview . . . . . . . . . . . Organizing Straight Line Code . . . . . . . . . . . Using Conditionals . . . . . . Unusual Control Structures Taming Deep Nesting Organizing Straight Line Code Statement order can be one of following categories • must be a specific order • order doesn’t matter . Sample of straight line codes .. ...... Foo () ; HelloWorld () ; f o r ( i n t i = 0; i < 100; i ++) { H e l l o K i t t y ( ) ; } 5 / 50
  • 6. Overview . . . . . . . . . . . Organizing Straight Line Code . . . . . . . . . . . Using Conditionals . . . . . . Unusual Control Structures Taming Deep Nesting With specific order . Run with specific order. The dependencies are obvious. .. ...... data = ReadData(); result = GetResultsFromData(data); PrintResults(results); 6 / 50
  • 7. Overview . . . . . . . . . . . Organizing Straight Line Code . . . . . . . . . . . Using Conditionals . . . . . . Unusual Control Structures Taming Deep Nesting With specific order . Run with specific order. The dependencies are not obvious. .. ...... revenue.ComputeMonthly(); revenue.ComputeQuarterly(); revenue.ComputeAnnual(); 7 / 50
  • 8. Overview . . . . . . . . . . . Organizing Straight Line Code . . . . . . . . . . . Using Conditionals . . . . . . Unusual Control Structures Taming Deep Nesting With specific order Make the dependences obvious. • Organize code • Name routine • Use routine parameters • Document dependencies with comments • Check dependencies with assertions or error-handling 8 / 50
  • 9. Overview . . . . . . . . . . . Organizing Straight Line Code . . . . . . . . . . . Using Conditionals . . . . . . Unusual Control Structures Taming Deep Nesting With specific order . With specific order, but not obviously. .. ...... ComputeMarketingExpense () ComputeSalesExpense () ComputeTravelExpense () ComputePersonnelExpense () DisplayExpenseSummary () • The ComputeMarketingExpense() will initialize the expense. • The dependencies are not obvious in above codes. 9 / 50
  • 10. Overview . . . . . . . . . . . Organizing Straight Line Code . . . . . . . . . . . Using Conditionals . . . . . . Unusual Control Structures Taming Deep Nesting With specific order • The parameter expense gives a hint the following routines are grouped. • The names of InitialExpenseData() and DisplayExpenseSummary() are obvious executed at first and last. . Grouped with routine parameter .. ...... I n i t i a l E x p e n s e D a t a ( expense ) ; ComputeMarketingExpense ( expense ) ; ComputeSalesExpense ( expense ) ; ComputeTravelExpense ( expense ) ; ComputePersonalExpense ( expense ) ; DisplayExpenseSummary ( expense ) ; 10 / 50
  • 11. Overview . . . . . . . . . . . Organizing Straight Line Code . . . . . . . . . . . Using Conditionals . . . . . . Unusual Control Structures Taming Deep Nesting With specific order . Document dependencies with comments .. ...... /∗∗ ∗ Compute expense data . Each of the r o u t i n e s a c c e s s e s ∗ the member data expenseData . DisplayExpenseSummary ∗ should be c a l l e d l a s t because i t depends on data ∗ c a l c u l a t e d by the other r o u t i n e s . ∗/ I n i t i a l E x p e n s e D a t a ( expense ) ; ComputeMarketingExpense ( expense ) ; ComputeSalesExpense ( expense ) ; ComputeTravelExpense ( expense ) ; ComputePersonalExpense ( expense ) ; DisplayExpenseSummary ( expense ) ; 11 / 50
  • 12. Overview . . . . . . . . . . . Organizing Straight Line Code . . . . . . . . . . . Using Conditionals . . . . . . Unusual Control Structures Taming Deep Nesting Statements whose order doesn’t matter • In the absence of routine dependencies, we can order statement or block of code ... • Keep related actions together. • Grouping related statements. • Ordering affects the readability, performance, maintainability. 12 / 50
  • 13. Overview . . . . . . . . . . . Organizing Straight Line Code . . . . . . . . . . . Using Conditionals . . . . . . Unusual Control Structures Taming Deep Nesting Keep related actions together . The related actions are not together, but jump around .. ...... MarketingData marketingData ; SalesData s a l e s D a t a ; TravelData t r a v e l D a t a ; t r a v e l D a t a . ComputeQuarterly () ; s a l e s D a t a . ComputeQuarterly () ; marketingData . ComputeQuarterly () ; s a l e s D a t a . ComputeAnnual () ; marketingData . ComputeAnnual () ; t r a v e l D a t a . ComputeAnnual () ; s a l e s D a t a . P r i n t () ; t r a v e l D a t a . P r i n t () ; marketingData . P r i n t () ; 13 / 50
  • 14. Overview . . . . . . . . . . . Organizing Straight Line Code . . . . . . . . . . . Using Conditionals . . . . . . Unusual Control Structures Taming Deep Nesting Keep related actions together . The related actions are together .. ...... MarketingData marketingData ; marketingData . ComputeQuarterly () ; marketingData . ComputeAnnual () ; marketingData . P r i n t () ; SalesData s a l e s D a t a ; s a l e s D a t a . ComputeQuarterly () ; s a l e s D a t a . ComputeAnnual () ; s a l e s D a t a . P r i n t () ; TravelData t r a v e l D a t a ; t r a v e l D a t a . ComputeQuarterly () ; t r a v e l D a t a . ComputeAnnual () ; t r a v e l D a t a . P r i n t () ; 14 / 50
  • 15. Overview . . . . . . . . . . . Organizing Straight Line Code . . . . . . . . . . . Using Conditionals . . . . . . Unusual Control Structures Taming Deep Nesting Grouping related statements 15 / 50
  • 16. Overview . . . . . . . . . . . Organizing Straight Line Code . . . . . . . . . . . Using Conditionals . . . . . . Unusual Control Structures Taming Deep Nesting Grouping related statements Bad grouped statements 16 / 50
  • 17. Overview . . . . . . . . . . . Organizing Straight Line Code . . . . . . . . . . . Using Conditionals . . . . . . Unusual Control Structures Taming Deep Nesting Grouping related statements Bad grouped statements Well grouped statements 17 / 50
  • 18. Overview . . . . . . . . . . . Organizing Straight Line Code . . . . . . . . . . . Using Conditionals . . . . . . Unusual Control Structures Taming Deep Nesting Key points • The strongest principle for organizing straight-line code is ordering dependencies. • Dependencies should be made obvious through the use of good routine names, parameter lists, comments. • If code doesn’t have order dependencies, keep related statements as close together as possible. 18 / 50
  • 19. Overview . . . . . . . . . . . Organizing Straight Line Code . . . . . . . . . . . Using Conditionals . . . . . . Unusual Control Structures Taming Deep Nesting Using Conditionals Using Conditionals: • if statements • case statements 19 / 50
  • 20. Overview . . . . . . . . . . . Organizing Straight Line Code . . . . . . . . . . . Using Conditionals . . . . . . Unusual Control Structures Taming Deep Nesting If statements Guidelines for If statements • Write the nominal path through the code first; then write the unusual cases. • Simplify complicated cases with boolean function calls. • Put the common cases first. • Make sure all cases are covered. 20 / 50
  • 21. Overview . . . . . . . . . . . Organizing Straight Line Code . . . . . . . . . . . Using Conditionals . . . . . . Unusual Control Structures Taming Deep Nesting If statements Write the nominal path through the code first; then write the unusual cases. . OpenFile ( i n p u t F i l e , s t a t u s ) ; i f ( s t a t u s == S t a t u s E r r o r ) { errorType = Fil eOpe nError ; // 1 , E r r o r Case } e l s e { ReadFile ( i n p u t F i l e , f i l e D a t a , s t a t u s ) ; // 2 , Normal Case i f ( s t a t u s == S t a t u s S u c c e s s ) { SummarizeFileData ( f i l e D a t a , summaryData , s t a t u s ) ; // 3 , Normal Case i f ( s t a t u s == S t a t u s E r r o r ) { errorType = ErrorTypeDataSummaryError ; // 4 , E r r o r Case } e l s e { PrintSummary ( summaryData ) ; // 5 , Normal case SaveSummaryData ( summaryData , s t a t u s ) ; i f ( s t a t u s == S t a t u s E r r o r ) { errorType = SummarySaveError ; // 6 , E r r o r case } e l s e { UpdateAllCounts () ; // 7 , Normal case EraseUndoFiles ( ) ; errorType = ErrorTypeNone ; } } } e l s e { errorType = F i l e R e a d E r r o r ; // } } 21 / 50
  • 22. Overview . . . . . . . . . . . Organizing Straight Line Code . . . . . . . . . . . Using Conditionals . . . . . . Unusual Control Structures Taming Deep Nesting If statements Write the nominal path through the code first; then write the unusual cases. . OpenFile ( i n p u t F i l e , s t a t u s ) ; i f ( s t a t u s == Status Suc cess ) { ReadFile ( i n p u t F i l e , f i l e D a t a , s t a t u s ) ; // 1 , Normal Case i f ( s t a t u s == S t a t u s S u c c e s s ) { SummarizeFileData ( f i l e D a t a , summaryData , s t a t u s ) ; // 2 , Normal Case i f ( s t a t u s == S t a t u s S u c c e s s ) { PrintSummary ( summaryData ) ; // 3 , Normal case SaveSummaryData ( summaryData , s t a t u s ) ; i f ( s t a t u s == StatusSuccess ) { UpdateAllCounts () ; // 4 , Normal case EraseUndoFiles ( ) ; errorType = ErrorTypeNone ; } e l s e { errorType = SummarySaveError ; // 5 , E r r o r case } } e l s e { errorType = ErrorTypeDataSummaryError ; // 6 , E r r o r Case } } e l s e { errorType = F i l e R e a d E r r o r ; // 7 , E r r o r Case } } e l s e { errorType = Fil eOpe nError ; // } 22 / 50
  • 23. Overview . . . . . . . . . . . Organizing Straight Line Code . . . . . . . . . . . Using Conditionals . . . . . . Unusual Control Structures Taming Deep Nesting If statements 1. Error Case 2. Normal Case 3. Normal Case 4. Error Case 5. Normal Case 6. Error Case 7. Normal Case 1. Normal Case 2. Normal Case 3. Normal Case 4. Normal Case 5. Error Case 6. Error Case 7. Error Case Easier to find the normal path through the codes. 23 / 50
  • 24. Overview . . . . . . . . . . . Organizing Straight Line Code . . . . . . . . . . . Using Conditionals . . . . . . Unusual Control Structures Taming Deep Nesting If statements Simplify complicated tests with boolean function calls . i f ( i n p u t C h a r a c t e r < SPACE ) { characterType = CharacterType ControlCharacter ; } e l s e i f ( i n p u t C h a r a c t e r == ’ ’ | | i n p u t C h a r a c t e r == ’ , ’ | | i n p u t C h a r a c t e r == ’ . ’ | | i n p u t C h a r a c t e r == ’ ! ’ | | i n p u t C h a r a c t e r == ’ ( ’ | | i n p u t C h a r a c t e r == ’ ) ’ | | i n p u t C h a r a c t e r == ’ : ’ | | i n p u t C h a r a c t e r == ’ ; ’ | | i n p u t C h a r a c t e r == ’ ? ’ | | i n p u t C h a r a c t e r == ’−’ ){ characterType = CharacterType Punctuation ; } e l s e i f ( ’ 0 ’ <= i n p u t C h a r a c t e r && i n p u t C h a r a c t e r <= ’ 9 ’ ) { characterType = C har a cterTyp e Dig it ; } e l s e i f ( ( ’ a ’ <= i n p u t C h a r a c t e r && i n p u t C h a r a c t e r <= ’ z ’ ) | | ( ’A ’ <= i n p u t C h a r a c t e r && i n p u t C h a r a c t e r <= ’Z ’ ) ) { characterType = C h a r a c t e r T y p e Le t t e r ; } 24 / 50
  • 25. Overview . . . . . . . . . . . Organizing Straight Line Code . . . . . . . . . . . Using Conditionals . . . . . . Unusual Control Structures Taming Deep Nesting If statements Simplify complicated tests with boolean function calls . With boolean function calls .. ...... i f ( I s C o n t r o l ( i n p u t C h a r a c t e r ) ) { characterType = CharacterType ControlCharacter ; } e l s e i f ( I s P u n c t u a t i o n ( i n p u t C h a r a c t e r ) ) { characterType = CharacterType Punctuation ; } e l s e i f ( I s D i g i t ( i n p u t C h a r a c t e r ) ) { characterType = C har a cterTyp e Dig it ; } e l s e i f ( I s L e t t e r ( i n p u t C h a r a c t e r ) ) { characterType = C h a r a c t e r T y p e Le t t e r ; } 25 / 50
  • 26. Overview . . . . . . . . . . . Organizing Straight Line Code . . . . . . . . . . . Using Conditionals . . . . . . Unusual Control Structures Taming Deep Nesting If statements Put the most common cases first. . Most common case first .. ...... i f ( I s L e t t e r ( i n p u t C h a r a c t e r ) ) { // The most common case characterType = C h a r a c t e r T y p e Le t t e r ; } e l s e i f ( I s P u n c t u a t i o n ( i n p u t C h a r a c t e r ) ) { characterType = CharacterType Punctuation ; } e l s e i f ( I s D i g i t ( i n p u t C h a r a c t e r ) ) { characterType = C har a cterTyp e Dig it ; } e l s e i f ( I s C o n t r o l ( i n p u t C h a r a c t e r ) ) { // The l e a s t common case characterType = CharacterType ControlCharacter ; } 26 / 50
  • 27. Overview . . . . . . . . . . . Organizing Straight Line Code . . . . . . . . . . . Using Conditionals . . . . . . Unusual Control Structures Taming Deep Nesting If statements Use default case to trap errors. . Trap the errors with default case. .. ...... i f ( I s L e t t e r ( i n p u t C h a r a c t e r ) ) { characterType = C h a r a c t e r T y p e Le t t e r ; } e l s e i f ( I s P u n c t u a t i o n ( i n p u t C h a r a c t e r ) ) { characterType = CharacterType Punctuation ; } e l s e i f ( I s D i g i t ( i n p u t C h a r a c t e r ) ) { characterType = C har a cterTyp e Dig it ; } e l s e i f ( I s C o n t r o l ( i n p u t C h a r a c t e r ) ) { characterType = CharacterType ControlCharacter ; } e l s e { // Trap the e r r o r s . D i s p l a y I n t e r n a l E r r o r ( ” Unexpected type of c h a r a c t e r detected . ” ) ; } 27 / 50
  • 28. Overview . . . . . . . . . . . Organizing Straight Line Code . . . . . . . . . . . Using Conditionals . . . . . . Unusual Control Structures Taming Deep Nesting Case Statements Choosing the Most Effective Ordering of Cases • Order cases alphabetically or numerically If cases are equally important, putting them in A-B-C order to improves readability. • Put the normal case first • Order cases by frequency Put the most frequently executed cases first and the least frequently executed last. • Human readers can find the most common cases easily. • Putting the common ones at the top of the code makes the search quicker. 28 / 50
  • 29. Overview . . . . . . . . . . . Organizing Straight Line Code . . . . . . . . . . . Using Conditionals . . . . . . Unusual Control Structures Taming Deep Nesting Case statements Tips of using case statements • Keep the actions of each case simple. Extract complicated codes to routine. • Use the default clause to detect errors. 29 / 50
  • 30. Overview . . . . . . . . . . . Organizing Straight Line Code . . . . . . . . . . . Using Conditionals . . . . . . Unusual Control Structures Taming Deep Nesting Case statements Tips of using case statements • Keep the actions of each case simple. Extract complicated codes to routine. • Use the default clause to detect errors. . ...... switch ( commandShortcutLetter ) { case ’ a ’ : PrintAnnualReport () ; break ; case ’ p ’ : // no a c t i o n r e q u i r e d , but case was c o n s i d e r e d break ; case ’ q ’ : P r i n t Q u a r t e r l y R e p o r t () ; break ; case ’ s ’ : PrintSummaryReport () ; break ; d e f a u l t : // Detect e r r o r s . D i s p l a y I n t e r n a l E r r o r ( ” I n t e r n a l E r r o r 905: C a l l customer support . ” ) ; } 30 / 50
  • 31. Overview . . . . . . . . . . . Organizing Straight Line Code . . . . . . . . . . . Using Conditionals . . . . . . Unusual Control Structures Taming Deep Nesting Case statements • Generally, code that falls through one case to another is an invitation to make mistake as the code is modified. It should be avoided. • Clearly and unmistakably identify the flow-through at the end of case statement. . ...... switch ( errorDocumentationLevel ) { case DocumentationLevel Full : D i s p l a y E r r o r D e t a i l s ( errorNumber ) ; // FALLTHROUGH −− F u l l documentation a l s o p r i n t s summary comments case DocumentationLevel Summary : DisplayErrorSummary ( errorNumber ) ; // FALLTHROUGH −− Summary documentation a l s o p r i n t s e r r o r number case DocumentationLevel NumberOnly : DisplayErrorNumber ( errorNumber ) ; break ; d e f a u l t : D i s p l a y I n t e r n a l E r r o r ( ” I n t e r n a l E r r o r 905: C a l l customer support . ” ) ; } 31 / 50
  • 32. Overview . . . . . . . . . . . Organizing Straight Line Code . . . . . . . . . . . Using Conditionals . . . . . . Unusual Control Structures Taming Deep Nesting Unusual Control Structure • Multiple returns from a routine • goto 32 / 50
  • 33. Overview . . . . . . . . . . . Organizing Straight Line Code . . . . . . . . . . . Using Conditionals . . . . . . Unusual Control Structures Taming Deep Nesting Multiple returns from a routine Multiple returns from a routine. • Use a return when it enhances readability. • Use guard clauses1 to simplify the complex error processing. 1 Check invalid conditions and return error code directly. 33 / 50
  • 34. Overview . . . . . . . . . . . Organizing Straight Line Code . . . . . . . . . . . Using Conditionals . . . . . . Unusual Control Structures Taming Deep Nesting Multiple returns from a routine . Multiple returns from a routine .. ...... Comparison Compare ( i n t value1 , i n t value2 ) { i f ( value1 < value2 ) { r e t u r n Comparison LessThan ; } e l s e i f ( value1 > value2 ) { r e t u r n Comparison GreaterThan ; } r e t u r n Comparison Equal ; } 34 / 50
  • 35. Overview . . . . . . . . . . . Organizing Straight Line Code . . . . . . . . . . . Using Conditionals . . . . . . Unusual Control Structures Taming Deep Nesting Multiple returns from a routine This codes can be re written with multiple returns... . Deep nesting .. ...... i f ( f i l e . validName () ) { i f ( f i l e . Open () ) { i f ( encryptionKey . v a l i d () ) { i f ( f i l e . Decrypt ( encryptionKey ) { // l o t s of statements // . . . } } } } 35 / 50
  • 36. Overview . . . . . . . . . . . Organizing Straight Line Code . . . . . . . . . . . Using Conditionals . . . . . . Unusual Control Structures Taming Deep Nesting Multiple returns from a routine . Use guard clauses to clarify the nominal cases .. ...... i f ( ! f i l e . validName () ) r e t u r n ; i f ( ! f i l e . open () ) r e t u r n ; i f ( ! encryptionKey . v a l i d () ) r e t u r n ; i f ( ! f i l e . Decrypt ( encryptionKey ) ) r e t u r n ; // l o t s of statements // . . . 36 / 50
  • 37. Overview . . . . . . . . . . . Organizing Straight Line Code . . . . . . . . . . . Using Conditionals . . . . . . Unusual Control Structures Taming Deep Nesting Multiple returns from a routine . More realistic codes. Use guard clauses to clarify the nominal cases .. ...... i f ( ! f i l e . validName () ) r e t u r n F i l e E r r o r I n v a l i d N a m e ; i f ( ! f i l e . open () ) r e t u r n F i l e E r r o r C a n t O p e n F i l e ; i f ( ! encryptionKey . v a l i d () ) r e t u r n F i l e E r r o r I n v a l i d E n c r y p t i o n K e y ; i f ( ! f i l e . Decrypt ( encryptionKey ) ) r e t u r n F i l e E r r o r C a n t D e c r y p t F i l e ; // l o t s of statements // . . . 37 / 50
  • 38. Overview . . . . . . . . . . . Organizing Straight Line Code . . . . . . . . . . . Using Conditionals . . . . . . Unusual Control Structures Taming Deep Nesting gotos About goto statements. • Generally, Without goto → High quality codes • Under some situations, goto → High readability and maintainability. 38 / 50
  • 39. Overview . . . . . . . . . . . Organizing Straight Line Code . . . . . . . . . . . Using Conditionals . . . . . . Unusual Control Structures Taming Deep Nesting gotos . Error processing and gotos .. e r r o r S t a t e = F i l e S t a t u s S u c c e s s ; f i l e I n d e x = 0; w h i l e ( f i l e I n d e x < numFilesToPurge ) { f i l e I n d e x += 1; i f ( ! F i n d F i l e ( f i l e L i s t ( f i l e I n d e x ) , f i l e T o P u r g e ) ) { e r r o r S t a t e = F i l e S t a t u s F i l e F i n d E r r o r ; goto End Proc ; } i f ( ! OpenFile ( f i l e T o P u r g e ) ) { e r r o r S t a t e = F i l e S t a t u s F i l e O p e n E r r o r ; goto End Proc ; } i f ( ! O v e r w r i t e F i l e ( f i l e T o P u r g e ) ) { e r r o r S t a t e = F i l e S t a t u s F i l e O v e r w r i t e E r r o r ; goto End Proc ; } i f ( ! Erase ( f i l e T o P u r g e ) ){ e r r o r S t a t e = F i l e S t a t u s F i l e E r a s e E r r o r ; goto End Proc ; } End Proc : D e l e t e P u r g e F i l e L i s t ( f i l e L i s t , numFilesToPurge ) ; 39 / 50
  • 40. Overview . . . . . . . . . . . Organizing Straight Line Code . . . . . . . . . . . Using Conditionals . . . . . . Unusual Control Structures Taming Deep Nesting Taming Deep Nesting • Few people can understand more than 3 level of nested if. 1986, Noam Chomsky, and Gerald Weinberg. • Many researchers recommend avoiding nesting more than 3 or 4 levels. Myers 1976, Marca 1981, and Ledgard and Tauer 1987a. 40 / 50
  • 41. Overview . . . . . . . . . . . Organizing Straight Line Code . . . . . . . . . . . Using Conditionals . . . . . . Unusual Control Structures Taming Deep Nesting Taming Deep Nesting . deep nesting if .. ...... i f ( i n p u t S t a t u s == I n p u t S t a t u s S u c c e s s ) { // l o t s of code . . . i f ( p r i n t e r R o u t i n e != NULL ) { // l o t s of code . . . i f ( SetupPage () ) { // l o t s of code . . . i f ( AllocMem ( &printData ) ) { // l o t s of code . . . } } } } 41 / 50
  • 42. Overview . . . . . . . . . . . Organizing Straight Line Code . . . . . . . . . . . Using Conditionals . . . . . . Unusual Control Structures Taming Deep Nesting Taming Deep Nesting . Simplify a nested if by retesting part of the condition .. i f ( i n p u t S t a t u s != I n p u t S t a t u s S u c c e s s ) goto EXIT ; // l o t s of code . . . i f ( p r i n t e r R o u t i n e == NULL ) goto EXIT ; // l o t s of code . . . i f ( ! SetupPage () ) goto EXIT ; // l o t s of code . . . i f ( ! AllocMem ( &printData ) ) goto EXIT ; // l o t s of code . . . EXIT : r e t u r n ; 42 / 50
  • 43. Overview . . . . . . . . . . . Organizing Straight Line Code . . . . . . . . . . . Using Conditionals . . . . . . Unusual Control Structures Taming Deep Nesting Taming Deep Nesting . Simplify a nested if by using a break block .. do { i f ( i n p u t S t a t u s != I n p u t S t a t u s S u c c e s s ) break ; // l o t s of code . . . i f ( p r i n t e r R o u t i n e == NULL ) break ; // l o t s of code . . . i f ( ! SetupPage () ) break ; // l o t s of code . . . i f ( ! AllocMem ( &printData ) ) break ; // l o t s of code . . . } w h i l e ( f a l s e ) ; 43 / 50
  • 44. Overview . . . . . . . . . . . Organizing Straight Line Code . . . . . . . . . . . Using Conditionals . . . . . . Unusual Control Structures Taming Deep Nesting Taming Deep Nesting . Overgrown decision tree .. ...... i f ( 10 < q u a n t i t y ) { i f ( 100 < q u a n t i t y ) { i f ( 1000 < q u a n t i t y ) { d i s c o u n t = 0 . 1 0 ; } e l s e { d i s c o u n t = 0 . 0 5 ; } } e l s e { d i s c o u n t = 0 . 0 2 5 ; } } e l s e { d i s c o u n t = 0 . 0 ; } 44 / 50
  • 45. Overview . . . . . . . . . . . Organizing Straight Line Code . . . . . . . . . . . Using Conditionals . . . . . . Unusual Control Structures Taming Deep Nesting Taming Deep Nesting . Convert to a set by if-then-elses .. ...... i f ( 1000 < q u a n t i t y ) { d i s c o u n t = 0 . 1 0 ; } e l s e i f ( 100 < q u a n t i t y ) { d i s c o u n t = 0 . 0 5 ; } e l s e i f ( 10 < q u a n t i t y ) { d i s c o u n t = 0 . 0 2 5 ; } e l s e { d i s c o u n t = 0; } 45 / 50
  • 46. Overview . . . . . . . . . . . Organizing Straight Line Code . . . . . . . . . . . Using Conditionals . . . . . . Unusual Control Structures Taming Deep Nesting Taming Deep Nesting . Convert to a set by if-then-elses .. ...... i f ( 1000 < q u a n t i t y ) { d i s c o u n t = 0 . 1 0 ; } e l s e i f ( ( 100 < q u a n t i t y ) && ( q u a n t i t y <= 1000 ) ) { d i s c o u n t = 0 . 0 5 ; } e l s e i f ( ( 10 < q u a n t i t y ) && ( q u a n t i t y <= 100 ) ) { d i s c o u n t = 0 . 0 2 5 ; } e l s e i f ( q u a n t i t y <= 10 ) { d i s c o u n t = 0; } 46 / 50
  • 47. Overview . . . . . . . . . . . Organizing Straight Line Code . . . . . . . . . . . Using Conditionals . . . . . . Unusual Control Structures Taming Deep Nesting Taming Deep Nesting . // p r o c e s s t r a n s a c t i o n depending on type of t r a n s a c t i o n i f ( t r a n s a c t i o n . Type == TransactionType Deposit ) { // p r o c e s s a d e p o s i t i f ( t r a n s a c t i o n . AccountType == AccountType Checking ) { i f ( t r a n s a c t i o n . AccountSubType == AccountSubType Business ) MakeBusinessCheckDep ( t r a n s a c t i o n . AccountNum , t r a n s a c t i o n . Amount ) ; e l s e i f ( t r a n s a c t i o n . AccountSubType == AccountSubType Personal ) MakePersonalCheckDep ( t r a n s a c t i o n . AccountNum , t r a n s a c t i o n . Amount ) ; e l s e i f ( t r a n s a c t i o n . AccountSubType == AccountSubType School ) MakeSchoolCheckDep ( t r a n s a c t i o n . AccountNum , t r a n s a c t i o n . Amount ) ; } e l s e i f ( t r a n s a c t i o n . AccountType == AccountType Savings ) MakeSavingsDep ( t r a n s a c t i o n . AccountNum , t r a n s a c t i o n . Amount ) ; e l s e i f ( t r a n s a c t i o n . AccountType == AccountType DebitCard ) MakeDebitCardDep ( t r a n s a c t i o n . AccountNum , t r a n s a c t i o n . Amount ) ; e l s e i f ( t r a n s a c t i o n . AccountType == AccountType MoneyMarket ) MakeMoneyMarketDep ( t r a n s a c t i o n . AccountNum , t r a n s a c t i o n . Amount ) ; e l s e i f ( t r a n s a c t i o n . AccountType == AccountType Cd ) MakeCDDep( t r a n s a c t i o n . AccountNum , t r a n s a c t i o n . Amount ) ; } e l s e i f ( t r a n s a c t i o n . Type == TransactionType Withdrawal ) { // p r o c e s s a withdrawal i f ( t r a n s a c t i o n . AccountType == AccountType Checking ) MakeCheckingWithdrawal ( t r a n s a c t i o n . AccountNum , t r a n s a c t i o n . Amount ) ; e l s e i f ( t r a n s a c t i o n . AccountType == AccountType Savings ) MakeSavingsWithdrawal ( t r a n s a c t i o n . AccountNum , t r a n s a c t i o n . Amount ) ; e l s e i f ( t r a n s a c t i o n . AccountType == AccountType DebitCard ) MakeDebitCardWithdrawal ( t r a n s a c t i o n . AccountNum , t r a n s a c t i o n . Amount ) ; } 47 / 50
  • 48. Overview . . . . . . . . . . . Organizing Straight Line Code . . . . . . . . . . . Using Conditionals . . . . . . Unusual Control Structures Taming Deep Nesting Taming Deep Nesting . Factor deeply nested code into its routine .. // p r o c e s s t r a n s a c t i o n depending on type of t r a n s a c t i o n i f ( t r a n s a c t i o n . Type == TransactionType Deposit ) { ProcessDeposit ( t r a n s a c t i o n . AccountType , t r a n s a c t i o n . AccountSubType , t r a n s a c t i o n . AccountNum , t r a n s a c t i o n . Amount ) ; } e l s e i f ( t r a n s a c t i o n . Type == TransactionType Withdrawal ) { ProcessWithdrawal ( t r a n s a c t i o n . AccountType , t r a n s a c t i o n . AccountNum , t r a n s a c t i o n . Amount ) ; } e l s e i f ( t r a n s a c t i o n . Type == TransactionType Transfer ) { MakeFundsTransfer ( t r a n s a c t i o n . SourceAccountType , t r a n s a c t i o n . TargetAccountType , t r a n s a c t i o n . AccountNum , t r a n s a c t i o n . Amount ) ; } e l s e { // p r o c e s s unknown t r a n s a c t i o n type LogTransactionError ( ”Unknown Transaction Type” , t r a n s a c t i o n ) ; } 48 / 50
  • 49. Overview . . . . . . . . . . . Organizing Straight Line Code . . . . . . . . . . . Using Conditionals . . . . . . Unusual Control Structures Taming Deep Nesting Taming Deep Nesting Summary of Techniques for Reducing Deep Nesting • Retest the part of condition. • Convert to if-then-elses. • Factor deeply nested code into its own routine. • Use objects and polymorphic dispatch. Design pattern. Ex, Strategy pattern, State pattern, ... etc. • ... etc. 49 / 50
  • 50. Overview . . . . . . . . . . . Organizing Straight Line Code . . . . . . . . . . . Using Conditionals . . . . . . Unusual Control Structures Taming Deep Nesting Ending Any questions ? 50 / 50