C program to find string length

This program prints length of string, for example consider the string "c programming" it's length is 13. Null character is not counted when calculating string length. To find string length we use strlen function of string.h.

C program to find string length

#include <stdio.h>
#include <string.h>
 
int main()
{
   char a[100];
   int length;
 
   printf("Enter a string to calculate it's length\n");
   gets(a);
 
   length = strlen(a);
 
   printf("Length of entered string is = %d\n",length);
 
   return 0;
}

Download String length program.
Output of program:

You can also find string length using pointer or without strlen function. Following program shows how to achieve this.

C program to find string length without strlen

C program to find length of a string using pointers.

#include <stdio.h>
 
int main()
{
   char array[100], *pointer;
   int length = 0;
 
   printf("Enter a string\n");
   gets(array);
 
   pointer = array;
 
   while(*(pointer+length))
      length++;
 
   printf("Length of entered string = %d\n",length);
 
   return 0;
}

Function to find string length

int string_length(char *s)
{
   int c = 0;
 
   while(*(s+c))
      c++;
 
   return c;
}

Reverse string

This program reverses a string entered by the user. For example if a user enters a string "reverse me" then on reversing the string will be "em esrever". We show you three different methods to reverse string the first one uses strrev library function of string.h header file and in second we make our own function to reverse string using pointers, reverse string using recursion and Reverse words in string. If you are using first method then you must include string.h in your program.

C programming code

/* String reverse in c*/

#include <stdio.h>
#include <string.h>
 
int main()
{
   char arr[100];
 
   printf("Enter a string to reverse\n");
   gets(arr);
 
   strrev(arr);
 
   printf("Reverse of entered string is \n%s\n",arr);
 
   return 0;
}

Download Reverse string program.
Output of program:

/* Second method */

C program to reverse a string using pointers

: Now we will invert string using pointers or without using library function strrev.

#include<stdio.h>
 
int string_length(char*);
void reverse(char*);
 
main() 
{
   char string[100];
 
   printf("Enter a string\n");
   gets(string);
 
   reverse(string);
 
   printf("Reverse of entered string is \"%s\".\n", string);
 
   return 0;
}
 
void reverse(char *string) 
{
   int length, c;
   char *begin, *end, temp;
 
   length = string_length(string);
 
   begin = string;
   end = string;
 
   for ( c = 0 ; c < ( length - 1 ) ; c++ )
      end++;
 
   for ( c = 0 ; c < length/2 ; c++ ) 
   {        
      temp = *end;
      *end = *begin;
      *begin = temp;
 
      begin++;
      end--;
   }
}
 
int string_length(char *pointer)
{
   int c = 0;
 
   while( *(pointer+c) != '\0' )
      c++;
 
   return c;
}

C program to reverse a string using recursion

#include <stdio.h>
#include <string.h>
 
void reverse(char*, int, int);
 
int main()
{
   char a[100];
 
   gets(a);
 
   reverse(a, 0, strlen(a)-1);
 
   printf("%s\n",a);
 
   return 0;
}
 
void reverse(char *x, int begin, int end)
{
   char c;
 
   if (begin >= end)
      return;
 
   c          = *(x+begin);
   *(x+begin) = *(x+end);
   *(x+end)   = c;
 
   reverse(x, ++begin, --end);
}

In recursion method we swap characters at the begin and at the end and then move towards the middle of the string. This method is inefficient due to repeated function calls but useful in practicing recursion.