C Program to Check whether the Given String is a Palindrome

Palindrome is a string, which when read in both forward and backward way is same.

Example:

radar, madam, pop, lol, etc.

Palindrome String Check Program in C

Example:

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

int main(){
    char string1[20];
    int i, length;
    int flag = 0;
    
    printf("Enter a string:");
    scanf("%s", string1);
    
    length = strlen(string1);
    
    for(i=0;i < length ;i++){
        if(string1[i] != string1[length-i-1]){
            flag = 1;
            break;
           }
        }
    
    if (flag) {
        printf("%s is not a palindrome", string1);
    }    
    else {
        printf("%s is a palindrome", string1);
    }
    return 0;
}

Program Output:

Explanation:

To check if a string is a palindrome or not, a string needs to be compared with the reverse of itself.

Consider a palindrome string: radar,

---------------------------
index: 0 1 2 3 4

value: r a d a r
---------------------------

To compare it with the reverse of itself, the following logic is used:

1. 0th character in the char array, string1 is same as 4th character in the same string.
2. 1st character is same as 3rd character.
3. 2nd character is same as 2nd character.
4. . . . .
5. ith character is same as 'length-i-1'th character.
6. If any one of the above condition fails, flag is set to true(1), which implies that the string is not a palindrome.
7. By default, the value of flag is false(0). Hence, if all the conditions are satisfied, the string is a palindrome.