Check number input and ask it until he enters a number

Question

I want to check the user input if it is a number and I want the program to accept only a number as an input. I don't know if I explained myself clearly, I'll try by showing you an example:

int x;
printf("Write a number: ");
scanf("%d", &x);
while(!isdigit(x))
{
    printf("Not valid\n");
    fflush(stdin);
    scanf("%d", &x);
}

I tried using scanf("%d", &x) != 1 as a while condition but it remains inside the loop. Is there a way to ask an input until the user writes a number? For now I just return the function but I'd like not to.

`fflush(stdin);` now that's *bad*. Lookup why you should not flush `stdin`. — babon, Oct 21 '18 at 16:16

score 0 · Accepted Answer · answered Oct 21 '18 at 16:29

You have to check the return value of scanf():

#include <stdio.h>

int main(void)
{
    int x;
    while (printf("Write a number: "),
           scanf("%d", &x) != 1)  // when the number of successful conversion wasn't 1
    {
        fputs("Not valid!\n", stderr);
        int ch;
        while ((ch = getchar()) != EOF && ch != '\n');  // clear stdin from garbage
    }                                                   // that might be left.
}

Check number input and ask it until he enters a number

1 Answers1