strcmp return value is wrong (beginner)

Question

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

void getSentence(char userSentence[]);
int breakSentence_andCompare(char userSentence[] , char compareSentence[]);

#define MAX_SENTENCE 100

int main()
{
    int len = 0;
    char userSentence[MAX_SENTENCE] = {'o','k',0};
    char compareSentence[MAX_SENTENCE] = {'o',0};
    getSentence(userSentence);
    len = breakSentence_andCompare(userSentence,compareSentence);
}

/*
This function is asking the user to input info.
    input:user input string array - char userSentence[].
        output:none.
*/
void getSentence(char userSentence[])
{
    printf("Hello And Welcome To The Palindrome Cheker Made By xXTH3 SKIRT CH4S3RXx");
    printf("\nPlease Enter A Sentence: ");
    fgets(userSentence,MAX_SENTENCE,stdin);
}

/*
This function takes the input of the user and input it into another string backwards.
    input:user input string array - char userSentence[], backward user input string array - char compareSentence[].
        output:strcmp value.
*/
int breakSentence_andCompare(char userSentence[] , char compareSentence[])
{
    int i = 0;
    int z = 0;
    int len = 0;
    int cmp = 0;
    len = strlen(userSentence);
    len -= 1;
    for (i = len ; i >= 0 ; i--)
    {
        compareSentence[z] = userSentence[i];
        printf("%s",compareSentence);   
        z++;    
    }
    printf("\nuser: %s! compare: %s!",userSentence,compareSentence);
    cmp = strcmp(userSentence,compareSentence);
    printf("\n%d",&cmp);
    return cmp;
}

---

This program checks if inputted string is palindrome, To simply explain how it works:

1. It takes user input - String.
2. It Takes the user string and input is backwards in another string.
3. It compares the strings.

I have a really strange problem in the function and that's the strcmp return value. For some reason, when both strings have the same characters like ABBA the strcmp will return that the value of one of them is bigger. I'd really love to know what is the problem and how can I fix it.

P.S When I were searching the problem I thought that it might be connected to fact that the user input string might contain \n from the enter key; is that possible?

And please understand that this isn't a whole code. The code is missing the output part.

Answer 1

The problem is occurring because of trailing \n (newline) character in user input string.

fgets()

The fgets() function shall read bytes from stream into the array pointed to by s, until n-1 bytes are read, or a is read and transferred to s, or an end-of-file condition is encountered. The string is then terminated with a null byte. [EMPHASIS MINE]

So, a newline character makes fgets stop reading, but it is considered a valid character by the function and included in the input string.

Say, user input string is "ABBA". So, after entering the input the content of userSentence will be "ABBA\n".

In your program, you are reversing the input string and comparing it with the original input string.

After reversing, the content of compareSentence will be "\nABBA".

The content of both the strings are not same and the strcmp() will return non zero value as the comparison result.

There are various ways of removing trailing \n (newline) character from fgets() input. Check this.

Since you are a beginner, so one suggestion to you - Don't ignore the compiler warning('s).

For the statement -

printf("\n%d",&cmp);

You must be getting a warning message during compilation of your program.

You should try to identify the cause of warning message('s) and should resolve them.

There are much better ways to find out the whether a string is palindrome or not but since you are a beginner, your start is good. Happy Learning.. :)