String Operations (string.h)

C language recognizes that string is a different class of array by letting us input and output the array as a unit and are terminated by null character. C library supports a large number of string handling functions that can be used to carry out many of the string manipulations such as :-

 * Length (Number of character in the string).
 * Concatenation (Adding two or more strings).
 * Comparing two strings.
 * Substring (Extract substring from a given string).
 * Copy (Copies one string over another).

To do all the operation described here it is essential to include string.h library header file in the program.

strlen( ) Function
  This function counts and returns the number of character in a string. The length does not include a null character.

 Syntax
 n=strlen(string);
                     Where n is integer variable which receives the value of length of the string.

Example :
  length = strlen("Irawen");
The function will assign number of character 9 in the string to a integer variable length.


\*Write a C program to find the length of the string using strlen( ) function. */

#include<stdio.h>
#include<string.h>
void main( )
{
char name[100];
int length;
printf("Enter the string");
gets(name);
length = strlen(name);
printf("\n Number of character in the string is=%d",length);
}

strcat( ) Function
 When you combine two strings , you add the character of one string to the end of other string. The process is called concatenation. The strcat( ) function joins two strings together. It takes the following form

Syntax :
  strcat(string1, string2)
   String1 and string2 are character arrays. When the function strcat is executed string2 is appended to string1. The string2 remains unchanged.

Example :
 strcpy(string1, "sri");
 strcpy(string2,"Bhagavan");
 printf("%s",strcat(string1,string2);
  
From the above program segment the value  of string1 becomes sribhagavan. The string at str2 remains unchanged as bhagavan.

strcmp( ) Function
  In C language we cannot directly compare the value of 2 strings in a condition like if(string1==string2).
  
Most libraries however contain the strcmp( ) function, which returns a zero if 2 strings are equal, or a non zero number if the strings are not the same. The syntax of strcmp( ) is given below :
       Strcmp(string1,string2)

 String1 and string2 may be string variable or string constants. String1 and string2 may be string variable or string constant some computers return a negative if the string1 is alphabetically less than the second and a positive number if the string is greater than the second.

Example :
strcmp("Newyork","Newyork")  will return zero because 2 strings are equal.

strcmp("their","there") will return a 9 which is the numeric difference between ASCII 'i' and ASCII 'r'.

strcmp("The","the") will return 32 which is the numeric difference between ASCII "T" & "t".


strcmpi( ) Function 
  This function is same as strcmp( ) which compares 2 string but not case sensitive.

Example :
  strcmpi("THE","the");  will return 0;

strcpy( ) Function
  C language not allow you to assign the characters to a string directly as in the statement name="Robert";

Instead use the strcpy( ) function found in most compilers the syntax of the function is illustrated below.
 strcpy(string1,string2);

Strcpy function assign the contents of string2 to string1. String2 may be a character array variable or a string constant.

strcpy(Name,"Robert");
In the above example Robert is assigned to the string called name.

strlwr( ) Funtion
 This function converts all characters in a string from uppercase to lower case.

Syntax:
 strlwr(string);

For example :
strlwr("IRAWEN") converts to Irawen.


strrev( ) Function
  This function reverses the character in a string.

Syntax
  strrev(string);

For example :
strrev("program") reverses the character in a string into "margrop".

strupr( ) Function
  This function converts all character in a string from lower case to uppercase.

Syntax
 strupr(string);

For example :
 strupr("pirawen") will convert the string to PIRAWEN.

/* Example program to use string functions */

#include<stdio.h>
#include<string.h>
void main( )
{
char s1[20], s2[20], s3[20];
int x;
printf("Enter the strings");
scanf("%s%s",s1,s2);
x=strcmp(s1,s2);
if(x!=0)
{
printf("\nStrings are not equal\n");
strcat(s1,s2);
}
else
printf("\nStrings are equal");
strcpy(s3,s1);
l1=strlen(s1);
l2=strlen(s2);
l3=strlen(s3);
printf("\n s1=%s\t length=%d characters\n",s1,l1);
printf("\n s2=%s\t length=%d characters\n",s2,l2);
printf("\n s3=%s\t length=%d characters\n",s3,l3);
}