While loop never stops when I enter a character in a place

Question

I have a problem with this loop when I enter a character for ˋscanfˋ. The loop will never stop. But when I enter a number all works good.

This Is The Code:

#include <stdio.h>
#include <stdlib.h>

int main() {

    int x;

    printf("Enter 1 Or 2\n");
    scanf("%i",&x);

    while (x!=1 && x!=2) {

        printf("Please Enter A Right Value \n");
        scanf("%i",&x);
    }

    printf("Finish");
}

@TusharWalzade No, he wants it to repeat until you enter a valid input. — Barmar, Dec 29 '17 at 12:08
Have you understood it? I have explained it and check the edit. — user2736738, Dec 29 '17 at 13:22

user2736738 · Accepted Answer · 2017-12-29T12:35:45.753

Well when you input character, scanf actually tries to get those wrong character inputs from the stdin but as it is not as per the conversion specification provided it fails. And then it keeps those wrong input in the stdin. And next time the scanf fails again due to those wrong inputs. So you need to clear it before you attempt to get the input again using scanf. Also check the return value of scanf and in case it failed clear the stdin.

The provided code checks for EOF and also return value of scanf the standard says explicitly about the return value of scanf :-

7.21.6.2p16

The fscanf function returns the value of the macro EOF if an input failure occurs before the first conversion (if any) has completed. Otherwise, the function returns the number of input items assigned, which can be fewer than provided for, or even zero, in the event of an early matching failure.

The code will be something like this. (This is using scanf).

Better even use fgets. you can easily and more better way control the erro neous inputs. With fgets you will read the entire line and then parse the integer input from it using strtol or strtoul. Yes in case of integer input there will be a case there also - you need to check if the parsed long or unsigned long is of proper size so that they can be kept in int variable.

@Ron.: I see..but this is clearly understandable...I wil try to explain more clearly. — user2736738, Dec 29 '17 at 12:16

While loop never stops when I enter a character in a place

1 Answers1