using fgets and strcmp in C

Question

I'm trying to get a string input from the user and then run different functions depending on the input they've entered.

For example, say I asked, "What is your favorite fruit?" and I want the program to comment depending on what they enter...I'm not sure how to do this. Here's what I have so far:

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

char fruit[100];

main() {
    printf("What is your favorite fruit?\n");
    fgets (fruit, 100, stdin);
    if (strcmp(fruit, "apple")) {
        printf("Watch out for worms!\n");
    }
    else {
        printf("You should have an apple instead.\n");
        }

}

When I run the program, no matter what I enter, it never does the else statement.

Thanks for your help!

`strcmp` returns `0` (which will evaluate as false) to indicate that the two strings are equal. — Jerry Coffin, Aug 11 '13 at 04:26
Does it **really** hurt to read the documentation of the functions you are trying to use? — , Aug 11 '13 at 04:27

lulyon · Accepted Answer · 2013-08-11T07:33:43.937

Note two things in your code:

fgets keeps the trailing '\n'. the associated char in fruit should be replaced with a '\0' before comparing with the string "apple".
strcmp return 0 when two strings are the same, so the if clause should be changed based on what you mean.(The fruit and "apple" be equivalent in the if clause)
Standard usage of C main function is int main(){ return 0;}

The revised code:

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

char fruit[100];

int main() {
    printf("What is your favorite fruit?\n");
    fgets (fruit, 100, stdin);
    fruit[strlen(fruit)-1] = '\0';
    if (strcmp(fruit, "apple") == 0) {
        printf("Watch out for worms!\n");
    }
    else {
        printf("You should have an apple instead.\n");
    }
    return 0;
}

The above is the correct one, Because '\n' is taken by fgets as the end of string so replace it with '\0' is correct. — Madan Ram, Aug 11 '13 at 05:26

score 1 · Answer 2 · edited Aug 11 '13 at 06:16

1

Change the if condition to the following:

if(strcmp(fruit,"apple") == 0)

strcmp returns 0 strings if match. You should always compare the result using == operator

edited Aug 11 '13 at 06:16

Yu Hao

119,891
44
235
294

answered Aug 11 '13 at 04:31

Sarat

113
1
1
7

luser droog · Answer 3 · 2013-08-11T07:28:18.273

0

strcmp returns 0 if the inputs match, some value>0 if the left is "greater" than the right, some value<0 if the left is "lesser" than the right. So usually you want to simply test for equality with strcmp(...)==0. But there is also the clever version: !strcmp(...). Even if you don't use this style, it's useful to learn to recognize it.

And remember that fgets does not remove the newline character '\n' from the string.

edited Aug 11 '13 at 07:28

answered Aug 11 '13 at 04:25

luser droog

18,988
3
53
105

It removes if the length of string is `arraysize-1`. – 0decimal0 Aug 11 '13 at 04:42
1

Even then I wouldn't say that the newline is *removed*, but maybe *withheld* or *pending*. – luser droog Aug 11 '13 at 05:16
1

I should have used quotes around **removes** , It ain't the right word obviously ..... actually it retains `'\n'` if string is small enough for it to be accomodated otherwise it doesn't . – 0decimal0 Aug 11 '13 at 05:25
1

Note that your description of the return values of `strcmp()` is wrong; the values will be 0 on equality (you said that too), but when the first argument is 'smaller' than the second, the return value will just be negative, not necessarily -1; similarly, for 'greater', the return value will be positive, not necessarily +1. See [`strcmp()` behaviour in 32-bit and 64-bit systems](http://stackoverflow.com/questions/18095575/strcmp-behaviour-in-32-bit-and-64-bit-systems/18095632#18095632) – Jonathan Leffler Aug 11 '13 at 07:24

using fgets and strcmp in C

3 Answers3

Linked

Related