# While Loops

## Overview

We have already [covered](../if/README.md) the `if` statement. A `while` loop is exactly the same with the addition of at least one branch and a label. It really is that simple.

To illustrate this, here is a flow chart of an `if` statement (on the left) compared to a `while` loop (on the right).

![while loop](./while.jpeg)

The closing brace in an `if` statement is indicated by the red arrow head. This isn't a branch, the code flow simply falls through to the statement beyond the closing brace. In the `while` loop, the behavior of the closing brace changes to be that of a branch back to just before the evaluation of the boolean condition (the "Decision").

A new label is placed before evaluating the "Decision". 

A new unconditional branch is placed after the end of the "Code Block."

For review, here is the assembly language for an `if` statement:

```asm
    // Assume value of a is in x0                                       // 1 
    // Assume value of b is in x1                                       // 2 
    cmp     x0, x1                                                      // 3 
    ble     1f                                                          // 4 
    // CODE BLOCK                                                       // 5 
1:                                                                      // 6 
```

Here is the code for the `while` showing one new label and one new unconditional branch:

```asm
    // Assume value of a is in x0                                       // 1 
    // Assume value of b is in x1                                       // 2 
                                                                        // 3 
 1: cmp     x0, x1                                                      // 4 
    ble     2f                                                          // 5 
    // CODE BLOCK                                                       // 6 
    b       1b                                                          // 7 
                                                                        // 8 
2:                                                                      // 9 
```

Temporary label `2` on `line 9` takes the place of the line after the closing brace in a `while` loop.