To check whether a string is a palindrome or not

palindrome.c

/**
  * A palindrome is a word, phrase, number or other sequence
  * of units that can be read the same way in either direction
  **/

#include<stdio.h>
#include<stdlib.h>
#include<string.h>

int main(void)
{
  int i, j, l;
  char str1[20], str2[20];

  printf("Enter any word:");
  scanf("%s", str1);

  /* Find the length of the string */
  l = strlen(str1);
  j = 0;

  /* Store the reversed string in another string str2 */
  for(i = l - 1; i >= 0; i-- )
    str2[j++] = str1[i];
  str2[j] = '\0';

  /* Compare str1 and str2 */
  /* strcmp returns 0 when the strings are equal, */
  /* a negative integer when s1 is less than s2, */
  /* or a positive integer if s1 is greater than s2, */
  /* according to the lexicographical order. */

  if(strcmp(str1, str2) == 0)
    printf("The word is a palindrome\n");
  else
    printf("The word is not a palindrome\n");

  return 0;
}

A string is palindrome, if string remains same after reversing it's character. For example, "madam" is a palindrome string whereas apple is not a palindrome string.