> For the complete documentation index, see [llms.txt](https://mrparkonline.gitbook.io/guide-to-high-school-computer-science/llms.txt). Markdown versions of documentation pages are available by appending `.md` to page URLs; this page is available as [Markdown](https://mrparkonline.gitbook.io/guide-to-high-school-computer-science/beginner-programming-grade-10-to-11/java-essentials/iterations/while-loops.md).

# While Loops

Loops are used in programming to repeat the execution of code instead of writing the line code of over and over again.

{% embed url="<https://www.youtube.com/watch?v=sKSIrz__d-M>" %}

### A Code Example

```java
int countdown = 5; 
while (countdown >= 0) {
    System.out.println(countdown);
    countdown--;
}
```

### Line by Line Analysis

```java
int countdown = 5
```

> We have set an outer variable to help us with our while loop.

```java
while (countdown >= 0)
```

> While is a keyword in java.
>
> It helps us start a looping structure.
>
> Much like an *if statement* a while loop will execute its code block when its *boolean expression* is true.
>
> Unlike an if statement, *a while loop will continue to execute its code block* as long as the **boolean expression is true**.

```
countdown--;
```

> This line of code just decrements countdown variable by 1 at every iteration.

### Formalization

**Iterations**: instructions or code being repeated until a specific end result is achieved.

**While Loop Format in Java**:

```java
while (condition) {
    // code to be executed repeatedly
}
```

**Infinite Loop:** An infinite loop is a while loop that never ends because the boolean condition of the loop never turns to false.

*Example:*

```java
String value = "Hello";
while (value.equals("Hello")) {
    System.out.println("Hello");
}
```

### Using While Loops as a Counter

```java
int counter = 0;
while (counter <= 10) {
    System.out.println("The counter is at: " + counter);
    counter++; // Incremental operator to increase a variable by 1.
}
```

By using some sort of a counting variable, you get to control the number of iterations you execute.

### Using a boolean variable to control when to end a while loop

```java
Scanner in = new Scanner(System.in);
String user_input = ""; // Declare an empty string
boolean loop = true;

while (loop == true) {
    System.out.println("Hello, World!");

    // Loop exiting code
    System.out.println("Would you like to end the loop? (Yes/No).");
    user_input = in.nextLine();
    if (user_input.equals("Yes")) {
        loop = false;
    }
}
```

We can also take an user input every iteration to check if they want to exit to prevent an infinite loop.