CODEWITHSUNDEEP
cstringloopsinput
John C.
John C.

Reputation: 445

Getting string input in C unless empty string is found

I am trying to get the user to enter string in a loop unless the string is found to be empty.

This is my attempt and I tried couple of different ways but I have the same problem. the loop keeps going even when I don't enter any thing.

Code 

char string[100];

do{
    fgets(string,100,stdin);
} while (string[0] != '\0');

Unfortunately, when I run this the output is something like this:

Output

> hello
> world
> test
>
>

I also tried using scanf() instead of fgets() but the same issue is still there.

Upvotes: 1

Views: 569

Answers (2)

Lion King
Lion King

Reputation: 33813

You can use strcmp function to check whether the input is empty or not:

char str[50];
while(strcmp(gets(str), "") != 0){
    printf("Output: %s\n", str);
}

strcmp function returns 0 when both strings are found to be identical.

Upvotes: 0

user3121023
user3121023

Reputation: 8286

Using fgets is pretty simple. As a feature, you can test to see it the input contains a newline. If not, there are pending characters.
scanf is possible using a scanset. %99[^\n] will scan up to 99 characters that are not a newline. %*c will consume the newline. If the only character is a newline then the scanset will fail and scanf will return 0. If more than 99 characters are entered, %*c will consume a character that is not a newline. fgets does not have that problem.

#include <stdio.h>

int main ( void) {
    char string[100] = "";
    int result = 0;

    printf ( "using fgets\nenter a blank line to stop\n");
    do {
        fgets ( string, sizeof string, stdin);
    } while ( string[0] != '\n');

    printf ( "using scanf\nenter a blank line to stop\n");
    do {
        result = scanf ( "%99[^\n]%*c", string);
    } while ( result == 1);

    return 0;
}

With ungetc, if scanf reads too many characters, the last character can be put back in the stream if it is not a newline.

    char last = 0;

    do {
        result = scanf ( "%99[^\n]%c", string, &last);
        if ( EOF == result) {
            fprintf ( stderr, "scanf EOF\n");
            return 0;
        }
        if ( '\n' != last) {
            ungetc ( last, stdin);
        }
    } while ( result == 2);

Upvotes: 1

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