What's wrong with cin >> num1, num2?

Question

#include 
using namespace std;

int main() {
  char choice;
  int solution, num1, num2;

  cout << \"Menu\";
  cout << \"\\n========\";
  cou         


        

Answer 1

int solution, num1, num2;

This leaves all variables uninitialised. Trying to read from them without a previous assignment is undefined behaviour.

cin >> num1, num2;

The supposed intention of this line is to read into both variables. What happens really is an application of the comma operator, with operands cin >> num1 on the left side and num2 on the right side.

The left side is evaluated and a value is written to num1; the second operand has no effect and leaves num2 in its uninitialised status.

It's as if you had written cin >> num1;.

solution = num1 + num2;

The aforementioned undefined behaviour happens, rendering your entire program invalid.

You can fix the problem as follows:

cin >> num1;
cin >> num2;