# While Loop

Repeat a block of code for as long as a condition stays true with C#'s while loop, and make sure the loop can end.

Novice · C# · Updated November 3, 2026

## After this lesson you can

- Repeat code while a condition is true with a while loop

## Key takeaways

- A `while` loop checks its condition before each iteration and runs its block only while the condition is `true`.
- Use `while` when you can't know in advance how many iterations it will take, such as the weeks of saving needed to reach a goal.
- Something inside the loop must make the condition `false`, or it's an infinite loop. Ctrl+C stops it.
- `Console.ReadLine()` waits for the user to type a line and returns it as a `string?`.

A **loop** runs the same block of code again and again. Loops are often used to work through every element of an array, but they do much more: count down, keep asking a question until the answer is right, add up savings week by week.

![A diagram of a loop: check the condition, run the block, and go back to check again](https://fsdtrainingmedia.blob.core.windows.net/public/images/2026/09/68ac1e8b680d4dafb96d2cf7b35d6d4e.png)

C# has four kinds of loop: `while`, `do-while`, `for` and `foreach`. This lesson is about the first.

## The while loop

A `while` loop checks a condition. If it's `true`, it runs the block, then goes back and checks again. When the condition is `false`, the loop ends and the program carries on after it.

```csharp
int countdown = 3;

while (countdown > 0)
{
    Console.WriteLine(countdown);
    countdown--;
}

Console.WriteLine("Liftoff!");
```

```text
3
2
1
Liftoff!
```

Each pass through the block is called an **iteration**. Here there are three: with `countdown` at 3, 2 and 1. When it reaches 0, `countdown > 0` is false and the loop ends.

## When you don't know how many times

`while` fits best when you can't know in advance how many iterations it'll take. How many weeks of saving $25 does it take to reach $180?

```csharp
decimal savings = 0;
decimal weeklyDeposit = 25m;
decimal goal = 180m;
int weeks = 0;

while (savings < goal)
{
    savings += weeklyDeposit;
    weeks++;
}

Console.WriteLine("Weeks needed: " + weeks);
Console.WriteLine("Savings: $" + savings);
```

```text
Weeks needed: 8
Savings: $200
```

## Asking until the answer is right

`Console.ReadLine()` waits for the user to type a line and press Enter, and returns what they typed as a `string`. A `while` loop can keep asking:

```csharp
Console.Write("Do you want to play? (yes/no) ");
string? answer = Console.ReadLine();

while (answer == "yes")
{
    Console.WriteLine("Playing...");
    Console.Write("Play again? (yes/no) ");
    answer = Console.ReadLine();
}

Console.WriteLine("Thanks for playing.");
```

- `Console.Write` prints without starting a new line, so the answer is typed on the same line as the question.
- `string?` is a `string` that might be `null`: no text at all. `ReadLine` returns `null` when there's nothing left to read, and the `?` says that's allowed. You'll learn more about it later; for now, use `string?` for what `ReadLine` returns.

Save it as `play.cs`, run it with `dotnet run play.cs`, and answer a few times. It keeps playing for as long as you type `yes`.

## Make sure it can end

Something inside the loop must eventually make the condition `false`. If nothing does, the loop never ends: an **infinite loop**.

```csharp
int countdown = 3;

while (countdown > 0)
{
    Console.WriteLine(countdown);
    // forgot countdown--; so countdown is 3 forever
}
```

This prints `3` forever. If your program seems frozen and its output keeps scrolling, press **Ctrl+C** in the terminal to stop it, then look for the line that should change the condition.

## Check yourself

2 questions to try on the lesson page.

## So what

A `while` loop repeats until something changes. Ask yourself two questions every time you write one: what keeps it going, and what makes it stop?

## Key terms

- [while Loop](https://www.ask-codey.com/glossary/while-loop-c-sharp)
- Iteration
- [Infinite Loop](https://www.ask-codey.com/glossary/infinite-loop-c-sharp)
- [Console.ReadLine()](https://www.ask-codey.com/glossary/console-readline)

## Cheat sheets

- [While Loop](https://www.ask-codey.com/cheat-sheets/looping-in-csharp-while-loop-cheat-sheet)

Source: https://www.ask-codey.com/lessons/looping-in-csharp-while-loop