使用C中的函数检查字符串是否是回文

Question

I want to check whether a string entered by the user is palindrome or not. Without using functions I have done this problem but when I use functions for this problem I am always getting the same output:

The Entered String Is Not Palindrome!

Even if the string entered by the user is palindrome I get the same output. Here is my code:

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

void reverse(char [],int);

int main() {
    char a[100];int len, i = 0;

    printf("Please enter the string to check: \n");
    fgets(a,100,stdin);

    //Loop to replace the '\n' inserted at the end of string due to fgets() with '\0'
    for (int i = 0; i < strlen(a); ++i)
    {
        if (a[i] == '\n')
        {
            a[i] = '\0';
        }
    }

    len = strlen(a);

    reverse(a,len);

    return 0;
}

void reverse(char b[100], int n) {
    char c[100];int k=0;

    //Read characters from b[] from the end and store them into c[]
    for (int i = n-1; i >= 0; i--)
    {
        c[k] +=b[i];
        k++;
    }
    c[k] = '\0';

    //Check if the reversed string c[] and the actual string b[] are equal
    if(strcmp(c,b) == 0)
        printf("The Entered String Is Palindrome!\n");
    else
        printf("The Entered String Is Not Palindrome!\n");
}

The code in the reverse() function is the same as the one I used to solve the same problem without functions(and that program worked perfectly fine). But still it isn't giving the correct output. What am I doing wrong here?

EDIT: Okay, so I have removed the c[k] += b[i] according to an users suggestion and now it works perfectly fine. But I still don't get it. I mean I used the same line in the same program, the only difference being I didn't use the functions concept there and it worked perfectly fine. Here is the code:

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

int main() {
    char a[100], b[100];
    int k=0;

    printf("Please enter the string: \n");
    fgets(a,100,stdin);

    //To replace the '\n' at the end of the string inserted by fgets()
    for (int i = 0; i < strlen(a); ++i)
    {
        if(a[i] == '\n')
            a[i] = '\0';
    }

    for (int i = strlen(a)-1; i >=0 ; i--)
    {
        b[k] += a[i];
        k++;
    }

    if (strcmp(a,b) == 0)
    {
        printf("The entered string is palindrome!\n");
    }
    else
        printf("The entered string is not palindrome! \n");

    return 0;
}

Is there some concept behind it that I am unaware of? If so then please enlighten me.

Answer 1

You invoked undefined behavior by using values of an uninitialized variable having automatic storage duration, which is indeterminate.

Instead of adding in c[k] +=b[i]; , just assign value from b as c[k] = b[i]; .