Fixing Warning C6031

"Warning C6031: return value ignored 'scanf'" in Visual Studio Community 2022:   

The caller doesn't check a function's return value for failure, and the called-function could return unexpected value.

#pragma warning(disable:4996)
#define _CRT_SECURE_NO_WARNINGS
#define _CRT_SECURE_NO_DEPRECATE  
#define _CRT_NONSTDC_NO_DEPRECATE

#include <stdio.h>

int gcd(int a, int b)
{
    if (!b) return a;
    return gcd(b, a % b);
}
int main(void)
{
    int a, b, c, t;

    printf("Enter 2 numbers: ");

    if (scanf("%d", &a) != 1)
    {
        printf("Error reading first number.\n");
        return 1;
    }

    if (scanf("%d", &b) != 1)
    {
        printf("Error reading second number.\n");
        return 1;
    }

    if (a <= b)
    {
        t = a; 
        a = b; 
        b = t; 
    }
    c = gcd(a, b);
    printf("最大公約数: %d\n", c);
    return 0;
}