Issues while inputting strings in C

Question

I am trying to write a C program that takes n as an integer input and then inputs n strings. The problem that when I run the program, it takes one input less than n. If I enter 1 as the first input the program just terminates. Here is the code :

int n;
scanf("%d", &n);
char str[101];

while (n--) {
    fgets(str, 101, stdin);
    // other stuff...
}

What am I doing wrong here?

score 3 · Answer 1 · answered Jul 10 '15 at 18:25

Your program will work if you use scanf() for the number and the string input.

#include <stdio.h>

int main()
{
    int n;
    char str[101];
    scanf("%d", &n);
    while (n--)
    {
        scanf("%s", str);
    }
    return 0;
}

But it's arguably better to use fgets() for all the inputs.

#include <stdio.h>

int main()
{
    int n;
    char str[101];
    fgets(str, 100, stdin);
    sscanf(str, "%d", &n);
    while (n--)
    {
        fgets(str, 100, stdin);
    }
    return 0;
}

I scarcely need to remind you since you used fgets() in the first place, you'll be aware that it retains the newline at the end of the input string.

Note: Better to use `fgets(str, sizeof str, stdin);` 1) is should be 101 not 100 and 2) avoid magic numbers. +1 for "better to use fgets() for all the inputs." — chux - Reinstate Monica, Jul 11 '15 at 04:43

score 1 · Answer 2 · answered Jul 10 '15 at 18:04

Remember that hitting the enter key sends a character to the stream too. Your program fails to account for this. Use the format scanf(%d%*c) to discard the second character.

int main(void) {

    int n;

    scanf("%d%*c", &n);

    char str[101];

    while (n--)
    {
        fgets(str, 101, stdin);

        // other stuff.....
    }

}

score 1 · Answer 3 · answered Jul 11 '15 at 14:11

int n;
scanf("%d", &n);
char str[101];

while (n--) 
{
fgets(str, 101, stdin);
// other stuff...
}

In this as you enter n and press ENTER from keyboard '\n is stored in stdin therefore as fgets encounters newline character if returns .

Therefore use this after scanf-

 char c ;
while((c=getchar())!=NULL && c!='\n');

Issues while inputting strings in C

3 Answers3