using fgets and strcmp in C [duplicate]

问题

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!

回答1:

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;
}

回答2:

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

回答3:

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.

来源：https://stackoverflow.com/questions/18168722/using-fgets-and-strcmp-in-c

标签

fgets

strcmp