C Program to Check if a String is a Palindrome without using the Built-in Function

This C Program checks a given string is palindrome without using the Built-in Function. This program first performs reverse of a string. Then it checks whether the given string is equivalent to the reversed string. If they are equal then the string is called as palindrome. The program doesn’t use any built-in function.

Here is source code of the C program to check a given string is palindrome without using the Built-in Function .The C program is successfully compiled and run on a Linux system. The program output is also shown below.

  1. /*
  2.  * C program to find the length of a string without using the
  3.  * built-in function also check whether it is a palindrome
  4.  */
  5. #include <stdio.h>
  6. #include <string.h>
  8. void main()
  9. {
  10.     char string[25], reverse_string[25] = {'\0'};
  11.     int i, length = 0, flag = 0;
  13.     printf("Enter a string \n");
  14.     gets(string);
  15.     /*  keep going through each character of the string till its end */
  16.     for (i = 0; string[i] != '\0'; i++)
  17.     {
  18.         length++;
  19.     }
  20.     printf("The length of the string '%s' = %d\n", string, length);
  21.     for (i = length - 1; i >= 0 ; i--)
  22.     {
  23.         reverse_string[length - i - 1] = string[i];
  24.     }
  25.    /*  Check if the string is a Palindrome */
  27.     for (flag = 1, i = 0; i < length ; i++)
  28.     {
  29.         if (reverse_string[i] != string[i])
  30.             flag = 0;
  31.     }
  32.     if (flag == 1)
  33.        printf ("%s is a palindrome \n", string);
  34.     else
  35.        printf("%s is not a palindrome \n", string);
  36. }

$ cc pgm53.c
$ a.out
Enter a string
how  are you
The length of the string 'how  are you' = 12
how  are you is not a palindrome
$ a.out
Enter a string
The length of the string 'madam' = 5
madam is a palindrome
$ a.out
Enter a string
The length of the string 'mam' = 3
mam is a palindrome

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If you wish to look at other example programs on Strings, go to C Programming Examples on Strings. If you wish to look at programming examples on all topics, go to C Programming Examples.
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