C++ CH3-P2 using c++ in all other parts.ppt

Copyright © 2012 Pearson Education, Inc.
Chapter 3 P2:
Loops

Outlines
3.2.1 Increment & Decrement Operators
3.2.2 Introduction to loops
3.2.3 Classification of loops
3.2.3.1 for loop
3.2.3.2 while loop
3.2.3.3 do-while loop
3.2.3.4 nested loop
3.2.4 Jumping Statements & their types
3.2.5 Continue statement & Break statement

3.2.1
The Increment and Decrement
Operators

Operators
• ++ is the increment operator.
It adds one to a variable.
val++; is the same as val = val + 1;
• ++ can be used before (prefix) or after (postfix) a
variable:
++val; val++;

Operators
• -- is the decrement operator.
It subtracts one from a variable.
val--; is the same as val = val - 1;
• -- can be also used before (prefix) or after
(postfix) a variable:
--val; val--;

Increment and Decrement
Operators in Program 5-1
Continued…

Increment and Decrement
Operators in Program 5-1

Prefix vs. Postfix
• ++ and -- operators can be used in
complex statements and expressions
• In prefix mode (++val, --val) the
operator increments or decrements, then
returns the value of the variable
• In postfix mode (val++, val--) the
operator returns the value of the variable,
then increments or decrements

Prefix vs. Postfix - Examples
int num, val = 12;
cout << val++; // displays 12,
// val is now 13;
cout << ++val; // sets val to 14,
// then displays it
num = --val; // sets val to 13,
// stores 13 in num
num = val--; // stores 13 in num,
// sets val to 12

Notes on Increment and Decrement
• Can be used in expressions:
result = num1++ + --num2;
• Must be applied to something that has a location
in memory. Cannot have:
result = (num1 + num2)++;
• Can be used in relational expressions:
if (++num > limit)
pre- and post-operations will cause different
comparisons

3.2.2
Introduction to loops

Introduction to Loops
• Loop: is a control structure that allows you to
repeat a block of code multiple times.
• This is useful when you want to perform
repetitive tasks, such as iterating over a range of
numbers or processing each item in a collection.
• The loop statements allow a set of instructions to
be performed repeatedly until a certain condition
is fulfilled

3.2.3
Classification of loops

Classification of Loops
There are several types of loops, each serving different use
cases:
1.for loop: Used when the number of iterations is known ahead
of time.
2.while loop: Used when the number of iterations is unknown,
and the loop continues as long as a condition remains true.
3.do-while loop: Similar to the while loop but guarantees that
the loop body executes at least once, as the condition is
checked after the loop body.
4.nested loop is a loop that exists within another loop. In other
words, you have one loop (inner loop) inside the body of
another loop (outer loop)

3.2.3.1
The For Loop

The for Loop
• Useful for counter-controlled loop
• General Format:
for(initialization; test; update)
statement; // or block in { }
• No semicolon after the update expression or
after the )

for Loop - Mechanics
for(initialization; test; update)
statement; // or block in
{ }
1) Perform initialization
2) Evaluate test expression
– If true, execute statement
– If false, terminate loop execution
3) Execute update, then re-evaluate test
expression

for Loop - Example
int count;
for (count = 1; count <= 5; count++)
cout << "Hello" << endl;

A Closer Look
at the Previous Example

Flowchart for the Previous Example

A for Loop in Program 5-9
Continued…

A for Loop in Program 5-9

A Closer Look at Lines 15 through
16 in Program 5-9

Flowchart for Lines 15 through 16
in Program 5-9

When to Use the for Loop
• In any situation that clearly requires
– an initialization
– a false condition to stop the loop
– an update to occur at the end of each iteration

The for Loop is a Pretest Loop
• The for loop tests its test expression
before each iteration, so it is a pretest
loop.
• The following loop will never iterate:
for (count = 11; count <= 10; count++)
cout << "Hello" << endl;

3.2.3.2
The while Loop

The while Loop
• General format of the while loop:
while (expression)
statement;
• statement; can also be a block of
statements enclosed in { }

The while Loop – How It Works
while (expression)
statement;
• expression is evaluated
– if true, then statement is executed, and
expression is evaluated again
– if false, then the loop is finished and
program statements following statement
execute

The Logic of a while Loop

The while loop in Program 5-3

How the while Loop in Program 5-
3 Lines 9 through 13 Works

Flowchart of the while Loop in
Program 5-3

The while Loop is a Pretest Loop
expression is evaluated before the
loop executes. The following loop will
never execute:
int number = 6;
while (number <= 5)
{
cout << "Hellon";
number++;
}

Watch Out for Infinite Loops
• The loop must contain code to make
expression become false
• Otherwise, the loop will have no way of
stopping
• Such a loop is called an infinite loop,
because it will repeat an infinite number of
times

Example of an Infinite Loop
int number = 1;
while (number <= 5)
{
cout << "Hellon";
}

3.2.3.3
The do-while Loop

The do-while Loop
• do-while: a posttest loop – execute the loop,
then test the expression
• General Format:
do
statement; // or block in { }
while (expression);
• Note that a semicolon is required after
(expression)

The Logic of a do-while Loop

An Example do-while Loop
int x = 1;
do
{
cout << x << endl;
} while(x < 0);
Although the test expression is false, this loop will
execute one time because do-while is a posttest
loop.

A do-while Loop in Program 5-7
Continued…

A do-while Loop in Program 5-7

do-while Loop Notes
• Loop always executes at least once
• Execution continues as long as
expression is true, stops repetition
when expression becomes false
• Useful in menu-driven programs to bring
user back to menu to make another choice
(see Program 5-8 on pages 245-246)

3.2.3.4
The nested Loop

Nested Loop
 A nested loop is a loop within another loop.
 This construct is useful for iterating over multiple dimensions
of data or performing repetitive tasks that require multiple
levels of iteration.
 Syntax
for (initialization1; condition1; increment1) {
for (initialization2; condition2; increment2) {
// Code to be executed
}
}

Example
#include <iostream>
using namespace std;
int main() {
for (int i = 1; i <= 10; i++) {
for (int j = 1; j <= 10; j++) {
cout << i * j << "t";
}
cout << endl;
}
return 0;
}

Explanation
1.Outer Loop: Iterates over rows (1 to 10).
2.Inner Loop: Iterates over columns (1 to 10) for each row.
3.Multiplication: Inside the inner loop, the product of i and j
is calculated and printed.
4.Newline: After each row, a newline character is printed to
move to the next line.

3.2.4
Jumping statements & Their Types

Breaking Out of a Loop
 In C++, jump statements are used to transfer control to
different parts of a program.
 These statements allow you to exit loops, skip over parts
of code, or move to a specific point within the program.
C++ provides four main types of jump statements:
1. break statement
2. continue statement
3. goto statement
4. return statement

3.2.5
Breaking and Continuing a Loop

Breaking Out of a Loop
The break statement is used to exit a loop or switch statement
immediately.
When a break statement is encountered, control jumps to the next
statement following the loop or switch. Example
•int main() {
• for (int i = 1; i <= 5; i++) {
• if (i == 3) {
• break; // exits the loop when i is 3
• }
• cout << i << " ";
• }
• return 0;
•}

The continue Statement
The continue statement skips the current iteration of a loop and
moves directly to the next iteration.
Unlike break, it does not terminate the loop but rather skips the
rest of the code in the current iteration. Example
•int main() {
• for (int i = 1; i <= 5; i++) {
• if (i == 3) {
• continue; // skips the rest of the loop when i is 3
• }
• cout << i << " ";
• }
• return 0;
•}

1 0
END

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