Handling of character strings C programming

INTRODUCTION
• A string is an array of characters
• Any group of characters defined between double
quotation marks is a constant string
– EXAMPLE: “Man is obviously made to think.”
• To include a double quote in the string to be
printed, use a back slash.
– EXAMPLE: printf(“Well Done !”);
– OUTPUT: Well Done!
– EXAMPLE: printf(“”Well Done!””);
– OUTPUT: “Well Done!”

INTRODUCTION
• Common operations performed on strings are:
– Reading and writing strings
– Combining strings together
– Copying one string to another
– Comparing strings for equality
– Extracting a portion of a string

DECLARING AND INITIALIZING
STRING VARAIBLES
• A string variable is any valid C variable name
and is always declared as an array
– SYNTAX: char string_name[size];
• The size determines the number of characters in
the string-name
– EXAMPLE: char city[10];
• When the compiler assigns a character string to
an character array, it automatically supplies a
null character (‘0’) at the end of the string
• The size should be equal to the maximum
number of characters in the string plus one

STRING VARAIBLES
• Character arrays may be initialized when they
are declared
char city[9] = “NEW YORK”;
char city[9] = (‘N’,’E’,’W’,’ ‘,’Y’,’O’,’R’,’K’,’0’);
• When we initialize a character by listing its
elements, we must supply the null terminator
• Can initialize a character array without
specifying the number of elements.

STRING VARAIBLES
• The size of the array will be determined
automatically, based on the number of elements
initialized.
char string[ ] = {'G','O','O','D','0'};
• Can also declare the size much larger than the
string size.
char str[10] = “GOOD”;
• Following will result in a compile time error.
char str[3] = “GOOD”;

STRING VARIABLES
• We cannot separate the initialization from declaration
– char str[5];
– str = “GOOD”;
• Following is not allowed
– char s1[4]=”abc”;
– char s2[4];
– s2 = s1;
• The array name cannot be used as the left operand
of an assignment operator

READING STRING FROM TERMINAL
• Reading words
– The input function scanf can be used with %s format
specification to read in a string of character
char address[15];
scanf(“%s”, address);
– The problem with the scanf function is that it
terminates its input on the first white space it finds
– A white space include blanks, tabs, carriage returns,
form feeds and new lines
INPUT: NEW YORK
– Only the string “NEW” will be read into the array
address
– In the case of character arrays, the ampersand (&) is
not required before the variable name
– The scanf function automatically terminates the string
with a null character

• C supports a format specification known as the
edit set conversion code %[..] that can be used
to read a line containing a variety of characters,
including whitespaces.
– char line[80];
– scanf(“%[^n]”,line);
– printf(“%s”,line);
• Will read a line of input from the keyboard and
display the same on the screen.

• Reading a Line of Text
– We have used getchar function to read a single
character from the terminal
– This getchar function is used repeatedly to read
successive single characters from the input and place
them into a character array
– Thus an entire line of text can be read and stored in
an array
– The reading is terminated when the newline character
(‘n’) is entered and the null character is then inserted
at the end of the string

PROGRAM
#include <stdio.h>
main()
{
char line[100], character;
int c;
c = 0;
printf("Enter Text:n");
do
{
character = getchar();
line[c] = character;
c++;
} while(character != 'n');
c = c-1;
line[c] = '0';
printf("n%sn",line);
}

READING A LINE OF TEXT
• For reading string of text containing whitespaces
is to use the library function gets available in the
<stdio.h>
gets(str)
• It reads characters into str from the keyboard
until a new-line character is encountered and
then appends a null character to the string.
char line[80];
gets(line)
printf(“%s”,line);
• The last two statements may be combined as:
printf(“%s”,gets(line));

READING A LINE OF TEXT
• Does not check array-bounds, so do not input
more characters, it may cause problems
• C does not provide operators that work on
strings directly.
• We cannot assign one string to another directly.
string2 = “ABC”
string1 = string2;
• Are not valid.
• To copy the characters in string2 into sting1, we
may do so on a character-by-character basis.

PROGRAM
#include<stdio.h>
main()
{
char string1[30], string2[30];
int i;
printf("Enter a stringn");
scanf("%s",string2);
for(i=0;string2[i]!='0';i++)
string1[i]=string2[i];
string1[i] = '0';
printf("n");
printf("%sn",string1);
printf("Number of characters = %dn",i);
}

WRITING STRINGS TO SCREEN
• The printf function with %s format is used to print
strings to the screen
• The format %s can be used to display an array
of characters that is terminated by the null
character
printf(“%s”, name);
• This display the entire content of the array name

USING PUTCHAR ANS PUTS
• C supports putchar to output the values of
character variables.
char ch = 'A';
putchar(ch);
• This statement is equivalent to
printf(“%c”,ch);
• Can use this function repeatedly to output string
of characters stored in an array using a loop.
char name[6] = “PARIS”;
for(i=0;i<5;i++)
putchar(name[i]);
putchar(“n”);

USING PUTCHAR ANS PUTS
• To print the string values is to use the function
puts declared in the header file <stdio.h>
puts(str);
• str is a string variable containing a string value.
• This printf the value of the string variable str and
then moves the cursor to the beginning of the
next line on the screen.
char line[80];
gets(line);
puts(line);
• Reads a line of text from the keyboard and
display it on the screen.

ARITHMETIC OPERATIONS ON
CHARACTERS
• C allows to manipulate characters the same way
we do with the numbers
• Whenever a character constant or character
variable is used in an expression, it is
automatically converted into an integer value by
the system
x = ‘a’;
printf(“%dn”,x);
OUTPUT: 97
EXAMPLE: x = ‘z’ – 1;
• The value of z is 122 and the above statement
assign 121 to the variable x

CHARACTERS
• Can use character constants in relational
expressions
EXAMPLE: ch >= ‘A’ && ch <= ‘Z’
• Test whether the character contained in the
variable ch is an upper-case letter
• Can convert a character digit to its equivalent
integer using
x = character – ‘0’;
• Where x is defined as an integer variable and
character contains the character digit
• The character containing the digit ‘7’ then
x = ASCII value of ‘7’ - ASCII value of ‘0’
= 55 – 48 = 7

CHARACTERS
• The C library supports a function that converts a
string of digits into their integer values
• The function takes the form
X = atoi(string)
• EXAMPLE:
number = “1998”;
Year = atoi(number);

PUTTING STRINGS TOGETHER
• We cannot assign the string to another directly
• We cannot join two strings together by the
simple arithmetic addition
string3 = strin1 + string2;
string2 = string1 + “hello”;
• The process of combining two strings together is
called concatenation

COMPARISON OF TWO STRINGS
• C does not permit the comparison of two strings
directly
if(name1 == name2)
if(name == “ABC”)
• are not permitted
• It is therefore necessary to compare the two
strings to be tested, character by character
• The comparison is done until a mismatch or one
of the strings terminates into a null character,
whichever occur first

COMPARISON OF TWO STRINGS
i=0;
while(str1[i]==str2[i] && str1[i] != '0' && str2 != '0')
i = i+1;
if(str1[i] == '0' && str2 == '0')
printf("strings are equal");
else
printf("strings are not equal");

Lengths of strings
/* Lengths of strings */
#include <stdio.h>
main()
{
char str1[] = "To be or not to be";
char str2[] = ",that is the question";
int count = 0; /* Stores the string length */
while (str1[count] != '0') /* Increment count till we reach the string */
count++; /* terminating character. */
printf("nThe length of the string1 is", count);
count = 0; /* Reset to zero for next string */
while (str2[count] != '0') /* Count characters in second string */
count++;
printf("nThe length of the string2 is", count);
}
OUTPUT:
The length of the string1 is 18
The length of the string2 is 21

STRING-HANDLING FUNCTIONS
• C library supports large number of string-
handling functions
• Some are

Strings
There are several standard routines that work on string variables.
Some of the string manipulation functions are,
strcpy(string1, string2); - copy string2 into string1
strcat(string1, string2); - concatenate string2 onto the end of string1
strcmp(string1,string2); - 0 if string1 is equals to string2,
< 0 if string1 is less than string2
>0 if string1 is greater than string2
strlen(string); - get the length of a string.
strrev(string); - reverse the string and result is stored in
same string.

strcat() FUNCTION
• The strcat function joins two strings together
– SYNTAX:
strcat(string1, string2);
• string1 and string2 are character array
• string2 is appended to string1
• The null character at the end of the string1 is
removed and string2 is placed from there
• The string2 remains unchanged

Example
#include <stdio.h>
#include <string.h>
int main ()
{
char src[50], dest[50];
puts(“Enter a text1”);
gets(src);
puts(“nEnter a text2”);
gets(dest);
strcat(dest, src);
printf("Final destination string : |%s|", dest);
}

C program to concatenate two strings without using strcat()
#include<stdio.h>
void main(void)
{
char str1[25],str2[25];
int i=0,j=0;
printf("nEnter First String:");
gets(str1);
printf("nEnter Second String:");
gets(str2);
while(str1[i]!='0')
i++;
while(str2[j]!='0')
{
str1[i]=str2[j];
j++; i++;
}
str1[i]='0';
printf("nConcatenated String is %s",str1);
}

strcmp() FUNCTION
• Compares two strings identified by the arguments and
has a value 0 if they are equal
• If they are not, it has the numeric difference between
the first non-matching characters in the strings
strcmp(string1, string2);
– EXAMPLE:
strcmp(nam1, name2);
strcmp(name1, “John”);
strcmp(“Rom”, “Ram”);
strcmp(“their”, ”there”);
• The above statement will return the value of -9 which
is numeric difference between ASCII “i” and ASCII “r”
is -9
• If the value is negative the string1 is alphabetically
above string2

#include <string.h>
#include<conio.h>
void main(void)
{
char str1[25],str2[25];
int dif,i=0;
clrscr();
printf("nEnter the first String:");
gets(str1);
printf("nEnter the secondString;");
gets(str2);
while(str1[i]!='0'||str2[i]!='0')
{
dif=(str1[i]-str2[i]);
if(dif!=0)
break;
i++;
}
if(dif>0)
printf("%s comes after
%s",str1,str2);
else
{
if(dif<0)
printf("%s comes after
%s",str2,str1);
else
printf("both the strings are same");
}
}

C program to compare two strings using strcmp
#include <stdio.h>
#include <string.h>
int main()
{
char a[100], b[100];
printf("Enter the first stringn");
gets(a);
printf("Enter the second stringn");
gets(b);
if( strcmp(a,b) == 0 )
printf("Entered strings are equal.n");
else
printf("Entered strings are not equal.n");
}

strcpy() FUNCITON
• Works almost like a string-assignment operator
– SYNTAX:
strcpy(string1, string2);
• Assigns the content of string2 to string1
– EXAMPLE:
strcpy(city, “DELHI”);
• Assign the string “DELHI” to the string variable
city
strcpy(city1, city2);
• Assigns the contents of the string variable city2
to the string variable city1

Copy String Manually without using strcpy()
#include <stdio.h>
int main()
{
char s1[100], s2[100], i;
printf("Enter string s1: ");
scanf("%s",s1);
for(i=0; s1[i]!='0'; ++i)
{
s2[i]=s1[i];
}
s2[i]='0';
printf("String s2: %s",s2);
}

strlen() FUNCTION
• This function counts and return the number of
characters in a string
– SYNTAX:
n = strlen(string);
• Where n is the integer variable which receives
the value of the length of the string
• The counting ends at the first null character
– EXAMPLE:
Ch = “NEW YORK”;
n = strlen(ch);
printf(String Length = %dn”, n);
– OUTPUT:
String Length = 8

TABLE OF STRINGS
• We use lists of character strings, such as
– List of name of students in a class
– List of name of employees in an organization
– List of places, etc
• These list can be treated as a table of strings and
a two dimensional array can be used to store the
entire list
– EXAMPLE:
student[30][15];
• is an character array which can store a list of 30
names, each of length not more than 15
characters
char city[ ][ ] = { “chandigarh”, “Madrad”, Ahmedab” };

ARRAYS OF STRINGS
• An array of strings is a two-dimensional
array. The row index refers to a particular
string, while the column index refers to a
particular character within a string.
Definition
char identifier[NO_OF_STRINGS][MAX_NO_OF_BYTES_PER_STRING];
Example
char name[5][31];

Initialization
char identifier[NO_OF_STRINGS][MAX_NO_OF_BYTES_PER_STRING] =
{ "initializer 1", "initializer 2", ... };
For example,
char name[5][31] = {“Logesh", "Jean", “ganesh", “moon",
“kumaran”};

Input and Output
Input
To accept input for a list of 5 names, we write
char name[5][31];
for (i = 0; i < 5; i++)
scanf(" %[^n]s", name[i]);
The space in the format string skips leading whitespace before
accepting the string.
Output
char name[5][31] = {"Harry", "Jean", "Jessica", "Irene", "Jim"};
printf("%s", name[2]);

Sorting of string
#include<stdio.h>
int main(){
int i,j,n;
char str[20][20],temp[20];
puts("Enter the no. of string to be sorted");
scanf("%d",&n);
for(i=0;i<=n;i++)
gets(str[i]);
for(i=0;i<=n;i++)
{ for(j=i+1;j<=n;j++){
{ if(strcmp(str[i],str[j])>0)
{
strcpy(temp,str[i]);
strcpy(str[i],str[j]);
strcpy(str[j],temp);
}
}
}
printf("The sorted stringn");
for(i=0;i<=n;i++)
puts(str[i]);
}

Search a name in a give list
#include<stdio.h> #include<string.h>
int main()
{
char name[5][10],found[10];
int j,i,flag=0;
printf("Enter a name :");
for(i=0;i<5;i++)
scanf("%s",name[i]);
printf("enter a searching stringn");
scanf("%s",found);
for(i=0;i<5;i++)
{
if(strcmp(name[i],found)==0)
{ flag=1; break; }
}
if(flag==1)
printf("String foundn");
else
printf("nString not found");
}

Handling of character strings C programming

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Handling of character strings C programming