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Practice

While Loop

When you need to repeatedly execute a block of code until a certain condition is met, you can use the while loop.

For example, using a while loop can be akin to "waiting for water to boil, and once it does, turning off the heat."

The while loop executes a block of code repeatedly as long as a given condition is true.


Structure of a while loop
while (condition) {
  // Code to be executed while the condition is true
}

Example 1: Counting Down​

Below is an example of counting down a number by 1 each time as long as the condition number > 0 is true.

Print numbers from 5 to 1
let number = 5;

while (number > 0) {
  console.log(number);
  number--;
}

In this example, console.log(number); is executed as long as number is greater than 0, and after each execution, the value of number is decreased by 1.


Example 2: Managing Budget​

Let's represent a scenario where you have $100 in your wallet and you keep buying $20 snacks until your money gets less than $30.

Snack buying code
let money = 100; // Initial amount of money in the wallet
let i = 0; // Initial count of snacks bought

// Repeat as long as the money is more than $30
while (money > 30) {
  i++; // Count of snacks bought
  money -= 20; // Subtract the price of the snack from the wallet
  console.log(i + ' time(s) after buying, $' + money + ' left');
}

console.log(`Remaining money: $${money}`);

Important Note on while Loops: Infinite Loops​

The most critical thing to watch out for when using a while loop is avoiding infinite loops.

An infinite loop occurs when the condition always remains true, causing the loop to run endlessly.

Such loops can stop your program from responding or consume excessive system resources.

For example, the following code falls into an infinite loop.

Example of an infinite loop
let number = 5;

while (number > 0) {
  console.log(number);
  // The value of number does not decrease, so the condition is always true
}

To avoid infinite loops, always ensure that within the loop, you modify a variable or component in such a way that the condition will eventually become false. Regularly review and test your code to ensure this.

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