C program to check if a given string is a palindrome

In this article, you will learn how to check whether a given string is a palindrome or not. Here is the list of programs available here:

But before going through these programs, let's talk about the meaning of a palindrome string.

What is a palindrome string?

Palindromes are strings in which all of the opposite characters are the same. And if any of the opposite characters mismatch, then the string is not a palindrome. For example:

In other words, you can say that if the reverse of a string is equal to its original, then that string can be called a palindrome string.

Palindrome String Program in C

The question is: write a program in C to enter any string at run-time and check whether it is a palindrome or not. The answer to this question is:

#include<stdio.h>
#include<conio.h>
#include<string.h>
int main()
{
    char str[50];
    int i, j, len, chk=0;
    printf("Enter any String (word): ");
    scanf("%s", str);
    len = strlen(str);
    for(i=0, j=(len-1); i<=(len-1); i++, j--)
    {
        if(str[i] != str[j])
        {
            chk=1;
            break;
        }
    }
    if(chk==1)
        printf("\nIt's not a Palindrome String");
    else
        printf("\nIt's a Palindrome String");
    getch();
    return 0;
}

The above program is written in the CodeBlocks IDE. Here is the output after building and running. This is the first screenshot of the first sample run:

c program check palindrome string

And here is the second screenshot of the first sample run:

c program string palindrome or not

As the reverse of fresherearth is rekcarcsedoc, which is not equal to the original string, that is fresherearth, therefore the string is not a palindrome.

Here is the first screenshot of the second sample run:

check string palindrome c program

Here in this case, the reverse of codoc is codoc, which is the same as the original string, that is, codoc, therefore, the string is a palindrome.

Program Explained

Here is another sample run for a palindrome string:

check palindrome string c program

And here is one more sample run, not a palindrome string:

palindrome string c program

Check palindrome strings in C without using the string function

Here is another program that will not use any string functions. As you can see from the previous program, the string function strlen() is used to find the length of the entered string. But here, this program will calculate the length of a string without using any library functions.

#include<stdio.h>
#include<conio.h>
int main()
{
    char str[50];
    int i, j, len, chk=0;
    printf("Enter any String (word): ");
    scanf("%s", str);
    len = 0;
    while(str[len]!='\0')
        len++;
    for(i=0, j=(len-1); i<=(len-1); i++, j--)
    {
        if(str[i] != str[j])
        {
            chk=1;
            break;
        }
    }
    if(chk==1)
        printf("\nIt's not a Palindrome String");
    else
        printf("\nIt's a Palindrome String");
    getch();
    return 0;
}

The code:

len=0;
while(str[len]!='\0')
   len++;

is used to find the length of a string. For example, if the user enters codes as input, 0 is initialized to len before entering the while loop. The '\0' is known as a null terminated character. At the end of every string, a null-terminated character gets automatically initialized. So the dry run of the above code works like this:

Check palindrome strings in C using the function

This is the last program to check whether a given string is a palindrome or not using a user-defined function.

#include<stdio.h>
#include<conio.h>
int checkPalindromeStr(char []);
int main()
{
    char str[50];
    int chk;
    printf("Enter any String (word): ");
    scanf("%s", str);
    chk = checkPalindromeStr(str);
    if(chk==1)
        printf("\nIt's not a Palindrome String");
    else
        printf("\nIt's a Palindrome String");
    getch();
    return 0;
}
int checkPalindromeStr(char str[])
{
    int i, j, len;
    len = 0;
    while(str[len]!='\0')
        len++;
    for(i=0, j=(len-1); i<=(len-1); i++, j--)
    {
        if(str[i] != str[j])
            return 1;
    }
    return 0;
}

This program will produce the same output as the first program given earlier in this article.

C Quiz


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