Multiply and divide

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

Multiply and divide

Now we will add multiply and divide functions to the calculator. Multiplication is simple with return a * b.

Division has a quirk: division by zero. In JavaScript, 5 / 0 gives Infinity, -5 / 0 gives -Infinity. This is usually unwanted.

So in the divide function, we first check whether the divisor is zero; if so, we return 0. This prevents the unexpected Infinity result.

Zero division check

In the divide(a, b) function, we first check b. If you write if (b === 0) return 0;, the function immediately returns 0 when the divisor is zero.

This is a technique called early return. If the condition holds, the rest of the function does not run; you write more readable code.

If not zero, normal division is done with return a / b;. This way the calculator runs safely.

Exercise Define multiply and divide

Define multiply(a, b) and divide(a, b) functions. multiply returns a * b; divide returns 0 if b === 0, otherwise a / b. add and subtract are already defined.

Show example solution

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

function subtract(a, b) {
  return a - b;
}

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

function divide(a, b) {
  if (b === 0) return 0;
  return a / b;
}

console.log(multiply(6, 7));
console.log(divide(10, 2));

Test yourself

Match the multiply/divide concepts

a * b

Multiplication
a / b

Division
b === 0

Zero check
return 0

Error case
What should the body of multiply(a, b) be?
- return a * b;
- return a + b;
- return a - b;
- return a / b;
Show answer

return a * b; — multiply does multiplication; returns a * b.

Zero check

if (____) return 0;

Show answer

if (b === 0) return 0;

Next lesson: process.argv

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