How to compare two strings in C?

Question

I want to compare 2 strings and if they're equil it should print something. I saw a post on this already but it doesn't work at me. Post: How to compare strings in an "if" statement?

Code:

int main(void) {

    char string[100];
    
    printf("Please enter something: ");
    fgets(string, 100, stdin);

    if (strcmp(string, "a") == 0)
        printf("a");

    else if (strcmp(string, "b") == 0)
        printf("b");

    else if (strcmp(string, "c") == 0)
        printf("c");

    else
        printf("something else");


    return (0);
}

It prints "something else" though I entered a.

The problem is most likely the newline that `fgets` includes in the buffer. — Some programmer dude, Mar 22 '21 at 09:17
In this case with string literals, you can simply use `memcmp(string, "a", sizeof("a")-1);` or similar. — Lundin, Mar 22 '21 at 09:26
"but it doesn't work at me" --> is is working and you are comparing strings correctly and they are not equal. It is just that the input string is not what you think it is. — chux - Reinstate Monica, Mar 22 '21 at 15:40

Vlad from Moscow · Answer 1 · 2021-03-22T09:24:18.283

2

The function fgets can append to the entered string the new line character '\n' that you should remove. For example

fgets(string, 100, stdin);
string[ strcspn( string, "\n" ) ] = '\0';

or

fgets(string, 100, stdin);
char *p = strchr( string, '\n' );
if ( p != NULL ) *p = '\0';

From the C Standard (7.21.7.2 The fgets function)

2 The fgets function reads at most one less than the number of characters specified by n from the stream pointed to by stream into the array pointed to by s. No additional characters are read after a new-line character (which is retained) or after end-of-file. A null character is written immediately after the last character read into the array.

edited Mar 22 '21 at 09:24

answered Mar 22 '21 at 09:18

Vlad from Moscow

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Thank you! What does the if statement part? – puncher Mar 22 '21 at 12:50
@puncher If the new line character '\n' is not found in the string then the function strchr returns a null pointer. – Vlad from Moscow Mar 22 '21 at 20:05

score 0 · Answer 2 · answered Mar 22 '21 at 10:29

The fgets() also takes in the newline character when the user presses the Enter key. So in order to remove that from what is stored in `string[100], just change :

fgets(string, 100, stdin);

to

strtok(fgets(string, 100, stdin), "\n");

to remove the newline character. Just make sure to include the #include <string.h> header

int main(void) {

    char string[100];
    
    printf("Please enter something: ");
    fgets(string, 100, stdin);

    if (strcmp(string, "a") == 0)
        printf("a");

    else if (strcmp(string, "b") == 0)
        printf("b");

    else if (strcmp(string, "c") == 0)
        printf("c");

    else
    {
        printf("something else - lets check why:\n Entered string:\n");
        for(size_t n = 0; n <= strlen(string); n++)
        {
            printf("string[%2zu] = ", n);
            switch(string[n])
            {
                case '\n':
                    printf("\\n");
                    break;
                case '\r':
                    printf("\\r");
                    break;
                case 0:
                    printf("null char");
                    break;
                default:
                    if(string[n] < ' ' || string[n] > 127)
                    {
                        printf("\\x%x", (unsigned)string[n]);
                    }
                    else
                    printf("'%c'", string[n]);
            }
            printf("\n");
        }
    }


    return (0);
}

https://godbolt.org/z/afb3Ej7E9

How to compare two strings in C?

3 Answers3

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