Solution to the first exercise in 'Grade 5 Lab' file.
corrected code:

int calculator(int x, int y, char z);

int main()
{
    int num1, num2, result;
    char op;

    printf("Please enter 2 numbers and operation between them:\n");
    scanf("%d%c%d", &num1, &op, &num2);

    result = calculator(num1, num2, op);
    if (result != 0)
        printf("result is %d\n", result);

    return 0;

}

int calculator(int num1, int num2, char op)
{
    switch (op)
    {
        case '+':
            return num1 + num2;
        case '-':
            return num1 - num2;
        case '*':
            return num1 * num2;
        case '/':
            if (num2 == 0)
                printf("Error: Division by zero\n");
            else return num1 / num2;
            return 0;
        default: printf("Error: Invalid operation\n");
            return 0;
    }
}