curriculum/challenges/english/blocks/lecture-working-with-loops/6732c06654ea3442724284fe.md
In previous lessons, you learned how to work with for loops, for...in loops and for...of loops. In this lesson, you will learn about the while loop and the do...while loop.
A while loop will run a block of code as long as the condition is true. Here is the basic syntax for a while loop:
while (condition) {
// code block to be executed
}
The condition is checked before the block of code is executed. If the condition is false, the block of code will not be executed.
while loops are useful when you do not know how many times you need to run the block of code. Here is an example of using a while loop:
:::interactive_editor
let counter = 0;
while(counter < 5) {
console.log(counter);
counter++;
}
:::
In this example, we have a variable called counter that is initialized to 0. The while loop will continue to run as long as the value of counter is less than 5. Inside the loop, we log the value of counter to the console and then increment counter by 1.
Another loop similar to the while loop would be the do...while loop. Here is the basic syntax:
do {
// code block to be executed
} while (condition);
One key difference between a do...while loop and a while loop is that the do...while loop will execute the block of code at least once before checking the condition.
If the condition is true, the block of code will continue to execute. If the condition is false, the block of code will stop executing.
Here is an example of using a do...while loop:
:::interactive_editor
let counter = 0;
do {
console.log(counter);
counter++;
} while (counter < 5);
:::
In this example, we have a variable called counter that is initialized to 0. The do...while loop will log the value of counter to the console and then increment counter by 1. After executing the block of code, it checks if the value of counter is less than 5. If it is, the loop will continue to run. If not, the loop will stop.
In most cases, you will probably use the while loop more often than the do...while loop. However, it is good to know both types of loops and when to use them.
What is the main difference between a while loop and a do...while loop?
A while loop executes the code block at least once, whereas a do...while loop does not.
Consider which loop executes its code block before checking the condition.
A do...while loop executes the code block at least once, whereas a while loop does not.
A while loop and a do...while loop are exactly the same and have no differences.
Consider which loop executes its code block before checking the condition.
A while loop checks the condition after executing the code block, whereas a do...while loop checks the condition before.
Consider which loop executes its code block before checking the condition.
2
In which situation would you prefer to use a do...while loop over a while loop?
When you need to execute a block of code zero or more times.
Think about which loop guarantees at least one execution of its code block.
When you need to execute a block of code at least once before checking the condition.
When the number of iterations is known beforehand.
Think about which loop guarantees at least one execution of its code block.
When you want to ensure the loop never executes.
Think about which loop guarantees at least one execution of its code block.
2
What happens if the condition in a while loop is initially false?
The code block inside the loop will execute once and then stop.
Review what occurs if the condition is not met at the start of a while loop.
The code block inside the loop will not execute at all.
The code block inside the loop will execute indefinitely.
Review what occurs if the condition is not met at the start of a while loop.
The loop will terminate immediately and produce an error.
Review what occurs if the condition is not met at the start of a while loop.
2