strcmp does not return 0 on equal strings in c

Question

So im making a program that checks if a word is a palindrome but when it comes to comparing the final strings at the end even if they are the same i get a -1 result edit: copy pasted the exact same code i used

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

int main()
{
    char input[50];
    char test[50];

    int ret;

    printf("Enter word or phrase to compare ");
    fgets(input,sizeof(input),stdin);
    strcpy(test,input);

    strrev(input);

    ret = strcmp(test,input);

    if(ret == 0)
        printf("\n this is a palindrome ");
    else
        printf("\n this is not a palindrome");
}

For input i used "ala" which i know is a palindrome i get the result

this is not a palindrome

Demonstration on IDEONE.

See [removing the newline from fgets](https://stackoverflow.com/questions/2693776) . — user3386109, Feb 06 '17 at 23:12
The newline doesn't matter for this particular purpose, because it is copied to `test` along with the rest of the string. — John Bollinger, Feb 06 '17 at 23:13
The program, as presently given, does not for me exhibit the problem described. — John Bollinger, Feb 06 '17 at 23:14
Try putting a newline at the end of the prompt `printf("Enter word or phrase to compare ");` — lost_in_the_source, Feb 06 '17 at 23:14
You have not posted the code where you have the alleged "get a -1 result". Please post the [Minimal, Complete, and Verifiable example](http://stackoverflow.com/help/mcve) that shows the problem. Show some examples of the input, the expected output, and the actual output. — Weather Vane, Feb 06 '17 at 23:16
You really could have saved us all alot of time if you had showed the real code from the beginning. Leaving out the call to `strrev` changed the whole question. — kaylum, Feb 07 '17 at 00:20
@user3386109 the newline would indeed be a good guess if in fact the code were not working. But the code present in the question at the time I made the comment worked just fine. — John Bollinger, Feb 07 '17 at 00:53

score 1 · Accepted Answer · answered Feb 06 '17 at 23:46

The problem is that you call strrev without stripping off the newline from your input obtained from fgets. This causes your reversed string to have the newline at the beginning of the string, which would cause a mismatch even if you intended to provide a palindrome as the input.

While there are various ways to achieve this, one way would be to look at the last byte of your input, and see if it is a newline character. If it is, remove it.

if (fgets(input,sizeof(input),stdin) == NULL) {
    /* todo: ... handle error ... */
    return 0;
}
len = strlen(input);
if (input[len-1] == '\n') input[--len] = '\0';
strcpy(test,input);

Actually, this question was [asked before](http://stackoverflow.com/q/20183687/315052). — jxh, Feb 07 '17 at 22:28

strcmp does not return 0 on equal strings in c

1 Answers1