How to check user's input data type in C? [duplicate]

Question

#define _CRT_SECURE_NO_WARNINGS
#include <stdio.h>
#include <stdlib.h>
void main()
{
int userNum;
int count=0;

printf("Please enter a whole number: ");
scanf("%i", &userNum);

while (userNum != 999)
{
    if (userNum > 0)
    {
        printf("Factors: ");
        for (count = 1; count <= userNum; count++)
        {
            if ((userNum % count) == 0)
            {
                printf("%i ", count);
            }
        }
    }
    else
    {
        printf("You input a negative number");
    }
    printf("\nPlease enter a whole number: ");
    scanf("%i", &userNum);
}
printf("\n");
system("pause");

}

Hey guys, that is my code for finding factors of a number given by the user. I have a problem: the program will run into an infinite loop if the user inputs a character or a double number. So, I want to ask how to solve that problem. I really like coding. Please help. Thank you so much.

Answer 1

Verify that the return value of scanf("%i", &userNum) is 1.

For example:

if (scanf("%i", &userNum) != 1) {
   // print some error and return from the function
}