For pset1 I want to reject an empty user input, so that when the user presses 'enter', either the Mario code runs or it gives the user an error message.

Pseudo code:

  1. printf ('message to input 1-23');
  2. scansf ('%i', &height);

  3. if (input <= 23 && input > 0)

{ ... a do/while (with 2 nested for) runs mario if input is 1-23. }

  1. else

{ printf ("prints error message if input isn't 1-23");}

This rejects numbers outside the range and all characters, but not empty spaces. I reckon there's an elegant solution to this (can fgets work? How?), but advice would be helpful at this point.

Question: How do I reject an empty user input?

1 Answer 1


Use GetInt() from the cs50 library!

GetInt(), as its name suggests, waits for an int input from the user and returns it.

You may use like that:

#include <cs50.h>
#include <stdio.h>

int main(void)
    // prompt the user for an int
    printf("Please give me an int:");
    int i = GetInt();

    printf("Thanks for the %d", i);
  • Thanks, Kareem. How would I implement that? And isn't it a bit problematic to rely on the cs50 library? I mean, it teaches us to solve the problem, but only within the cs50 application.
    – Fredrik
    Commented Jun 15, 2014 at 12:00
  • @Fredrik, Sorry! Messed things up 'cause I was on my phone! I was saying you don't need to implement nor to compile it. It's already written an compiled for you on the appliance! I just edited my answer with a sample code to show you how you can use it.
    – kzidane
    Commented Jun 15, 2014 at 12:15
  • Hmm. When I write it that way it gives me the following error: GetInt.c:(.text+0x16): undefined reference to 'GetInt' collect2: error: ld returned 1 exit status. Know what the problem is?
    – Fredrik
    Commented Jun 15, 2014 at 12:36
  • How are you compiling your program?
    – kzidane
    Commented Jun 15, 2014 at 12:37
  • gcc mario.c -o mario Should I use make instead?
    – Fredrik
    Commented Jun 15, 2014 at 12:41

You must log in to answer this question.

Not the answer you're looking for? Browse other questions tagged .