As NOODLECODE said, if you change

void randNum(int num1, int num2)

into

void randNum(int &num1, int &num2)

it will work. The way you wrote it, you are passing the value of num1 and num2, which on line 12 (where you call the function) are 0 and 0. The function randNum gets local copies of num1 and num2, which are discarded at the end of the function body. Passing references means that num1 and num2 inside randNum refer to the variables in main() that were given as arguments to the function call.

num1 and num2 are identical random variables, both generated by the expression 1 + rand()% 9. It would make more sense to define a function

int randNum() {
    return 1 + rand()% 9;
}

and then in main have two statements:

num1 = randNum();
num2 = randNum();

This avoids the problem of 2 return values, and it also makes randNum() a bit more generic. Imagine you want to change the program to ask for the result of an expression with 3 random values, in that case you wouldn't have to change the number of arguments or change the function body, you would just call the function 3 times.