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C Program to Check for Palindrome String



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In this article, you will learn and get about checking whether the given string is palindrome or not. Here are the list of programs available here:

But before going through these programs. Let's understand about the meaning of palindrome string.

What is Palindrome String ?

Those string whose all the opposite characters are same is palindrome. And if any of the opposite character mismatched, then the string is not 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 as 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 palindrome or not. The answer to this question is:

// Palindrome String Program in C
// -----codescracker.com-----

#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 under CodeBlocks IDE. Here is the output after build and run. This is the first screenshot of first sample run:

c program check palindrome string

And here is the second screenshot of first sample run:

c program string palindrome or not

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

Here is the first screenshot of second sample run:

check string palindrome c program

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

Program Explained

Here is another sample run for, a palindrome string:

check palindrome string c program

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

palindrome string c program

without using String Function

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

// Palindrome String Program in C without String function
// -----codescracker.com-----

#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 length of string. For example, if user enters codes as input, then initially 0 gets initialized to len before going to the while loop. The '\0' is known as null terminated character. At last of every string, a null terminated character gets automatically initialized. So the dry run of above code works like:

using Function

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

// Palindrome String Program in C using Function
// -----codescracker.com-----

#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 produced by first program given, earlier of this article. To learn more about function, refer to Function in C tutorial.

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