Multiply and divide

Add multiplication, division and the divide-by-zero check.

Multiply and divide

Now we will fill in the multiply and divide methods. Multiplication uses the * operator, division uses /.

The multiply body should be return a * b;. The divide body should be return a / b;. With these small changes, all four operations of the calculator work.

Because we use double, decimal results are preserved in division: 7.0 / 2.0 = 3.5. If we used int, the result would be 3 (truncated).

Division with double

In C++, division depends on the types of the operands. Dividing two int values gives an int: 7 / 2 = 3. Dividing two double values keeps the decimal: 7.0 / 2.0 = 3.5.

Since the calculator parameters are double, division works with decimals. Calling calc.divide(20, 4) returns 5; calling calc.divide(7, 2) returns 3.5.

The result is a single double value that can be printed with std::cout. In the next lesson we will handle division by zero.

Exercise Fill in multiply and divide

Change the multiply method body to return a * b; and the divide method body to return a / b;. The main already calls calc.multiply(6, 4); the output must be 24.

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 a * b; }
    double divide(double a, double b) { return a / b; }
};

int main() {
    Calculator calc;
    // Fill in multiply and divide with real arithmetic
    std::cout << calc.multiply(6, 4) << std::endl;
    return 0;
}

Test yourself

Match operators

+

Addition
-

Subtraction
*

Multiplication
/

Division
Which is the correct body for the multiply method?
- return a + b;
- return a * b;
- return a / b;
- return 0;
Show answer

return a * b; — The multiply method returns a * b.

Multiply body

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

Show answer

double multiply(double a, double b) { return a * b; }

Next lesson: Error handling

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