Multiply and divide

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

Multiply and divide

Now we will add multiply and divide functions. Multiplication uses *, division uses /.

Important: in Dart / always returns a double. So divide should return double: double divide(int a, int b) => a / b;.

For integer division you use ~/ (for example 10 ~/ 3 = 3). But in the calculator we want a decimal result, so we use /.

Exercise Add multiply and divide

Add the functions int multiply(int a, int b) => a * b; and double divide(int a, int b) => a / b; to the program. Inside main write print(multiply(5, 6)) and print(divide(10, 4)).

Show example solution

void main() {
  print('Calculator ready');
  print(add(3, 4));
  print(subtract(10, 3));
  print(multiply(5, 6));
  print(divide(10, 4));
}

int add(int a, int b) => a + b;
int subtract(int a, int b) => a - b;
int multiply(int a, int b) => a * b;
double divide(int a, int b) => a / b;

Divide-by-zero check

In division, if b is zero Dart returns Infinity as a double; it does not throw. But this is usually an unwanted result.

In a real calculator you want to prevent division by zero. You can add an if check: if (b == 0) { throw Exception('Divide by zero'); }.

In the next lesson we will see how to catch this thrown error with try/catch. For now, knowing the difference between ~/ and / is enough.

Test yourself

Which is the integer division operator?
```
10 ~/ 3 = 3
```
- /
- //
- %
- ~/
Show answer

~/ — ~/ does integer division.

Integer division

int result = 10 ____ 3;

Show answer

int result = 10 ~/ 3;

Match the operators

*

Multiplication
/

Division (double)
~/

Integer division
%

Modulo (remainder)

Next lesson: Error handling

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