Program to check whether string is palindrome or not without using library function
#include<stdio.h>
 void main()
{
            char s[20];
            int i=0, len, flag = 0;
            printf("\nEnter s1: ");
            gets(s);
            /*To
find the length of the string*/
            while(s[i]!='\0')
            {
                        i++;
            }
            len = i;
            for(i=0; i<len/2; i++)
            {
                        if(s[i] != s[len-i-1])
                        {
               
                    flag = 1;
               
                    break;
                        }
            }
            if(flag == 0)
                        printf("\nString is
palindrome.");
            else
                        printf("\nString is not
palindrome.");
}
Output:
Enter s1: abcba
Strings is palindrome.