Access violation error C

Question

I am a beginner and I am learning C and C++. I am trying to run this code in Visual Studio 2012 Express for Windows Desktop. This is a simple calculator code which I have written by myself! But whenever I run it I get this error Unhandled exception at 0x519600B4 (msvcr110d.dll) in Calculator.exe: 0xC0000005: Access violation writing location 0x00000000.

Forgive me for any mistakes (it is my first time). Thank you!

#include<stdio.h>
#include<conio.h>

main ()
{
    int num1, num2, result;
    char oper;
    scanf_s("%d%c%d", &num1, &oper, &num2);
    switch(oper)
    {
    case '+':
        result = num1 + num2;
        printf("%d", result);
        break;
    case '-':
        result = num1 - num2;
        printf("%d", result);
        break;
    case '*':
        result = num1 * num2;
        printf("%d", result);
        break;
    case '/':
        result = num1 / num2;
        printf("%d", result);
        break;
    default:
        printf("ERROR: INVALID OR UNRECOGNISED INPUT\n");
        break;
    }
    _getch();
}

Answer 1

When using scanf_s, for the %c format string you must specify how many characters you wish to read:

scanf_s("%d%c%d", &num1, &oper, 1, &num2);

The documentation describes the requirement:

Unlike scanf and wscanf, scanf_s and wscanf_s require the buffer size to be specified for all input parameters of type c, C, s, S, or string control sets that are enclosed in []. The buffer size in characters is passed as an additional parameter immediately following the pointer to the buffer or variable.