Add and subtract

Add and test the addition and subtraction functions.

Add and subtract

In the previous lesson you defined the Calculator skeleton; all methods returned 0. Now we will fill add and subtract with real arithmetic.

Inside a method body, the return statement sends the computed value back to the caller. For add you write return a + b;; for subtract write return a - b;.

The method body goes inside { }. A semicolon follows return. This small change makes the calculator actually work.

Method body and return

When a method is called, its body runs top to bottom. The return statement both returns a value and exits the method. Code after return does not run.

Example: calling calc.subtract(10, 3) sets a = 10, b = 3, and return a - b; gives 7. This value goes back to the caller.

The expression std::cout << calc.subtract(10, 3) first calls subtract, takes the returned 7 and prints it. This chaining is a common C++ pattern.

Exercise Fill in add and subtract

Change the add method body to return a + b; and the subtract method body to return a - b;. Leave multiply and divide as return 0; for now. The main already calls calc.subtract(10, 3); the output must be 7.

Show example solution

#include <iostream>

class Calculator {
public:
    double add(double a, double b) { return a + b; }
    double subtract(double a, double b) { return a - b; }
    double multiply(double a, double b) { return 0; }
    double divide(double a, double b) { return 0; }
};

int main() {
    Calculator calc;
    // Fill in add and subtract with real arithmetic
    std::cout << calc.subtract(10, 3) << std::endl;
    return 0;
}

Test yourself

Add body

double add(double a, double b) { return ____; }

Show answer

double add(double a, double b) { return a + b; }

What should the body of add(double a, double b) return?
- return a + b;
- return a;
- return 0;
- return b;
Show answer

return a + b; — The add method returns a + b.
Match method concepts

return a + b;

Addition result
return a - b;

Subtraction result
calc.subtract(10,3)

Returns 7
{ }

Method body

Next lesson: Multiply and divide

We Are Enhancing Your Experience

Cookie Preferences

Strictly Necessary Cookies

Analytical Cookies