# Loops

> Source: https://learn-typescript.org/loops/
> Part of Learn TypeScript, free to read.

### The for statement

JavaScript has two methods for running the same code several times. It is mainly used for iterating over arrays or objects. Let’s see an example:

```typescript
let i;
for (i = 0; i < 3; i = i + 1)
{
    console.log(i);
}
```

This will print out the following:

```typescript
0
1
2
```

The `for` statement in JavaScript has the same syntax as in Java and C. It has three parts:

  - **Initialization** - Initializes the iterator variable `i`. In this example, we initialize `i` to 0.

  - **Condition** - As long as the condition is met, the loop continues to execute. In this example, we check that `i` is less than 3.

  - **Increment** - A directive which increments the iterator. In our case, we increment it by 1 on every loop.

We can also write a shorter notation for the statement by inserting the variable definition inside the `for` loop and incrementing using the `++` operator.

```typescript
for (let i = 0; i < 3; i++)
{
    console.log(i);
}
```

To iterate over an array and print out all of its members, we usually use the `for` statement. Here’s an example:

```typescript
let myArray = ["A", "B", "C"];
for (let i = 0; i < myArray.length; i++)
{
    console.log("The member of myArray in index " + i + " is " + myArray[i]);
}
```

This prints out the contents of the array:

```typescript
The member of myArray in index 0 is A
The member of myArray in index 1 is B
The member of myArray in index 2 is C
```

Notice that we used the `length` property of an array, which returns the number of members in the array, so we know when to stop iterating.

### The while statement

The `while` statement is a more simple version of the `for` statement which checks if an expression evaluates to `true` and runs as long as it says `true`.

For example:

```typescript
let i = 99;
while (i > 0)
{
    console.log(i + " bottles of beer on the wall");
    i -= 1;
}
```

### break and continue statements

The `break` statement allows to stop the execution of a loop. For example, we can create a loop that loops forever using `while(true)` and use the `break` statement to break inside the loop instead by checking that a certain condition was met.

```typescript
let i = 99;
while (true)
{
    console.log(i + " bottles of beer on the wall");
    i -= 1;
    if (i == 0)
    {
        break;
    }
}
```

The `continue` statement skips the rest of the loop and jumps back to the beginning of the loop. For example, if we would want to print only odd numbers using a `for` statement, we can do the following:

```typescript
for (let i = 0; i < 100; i++)
{
    // check that the number is even
    if (i % 2 == 0)
    {
         continue;
    }
    // if we got here, then i is odd.
    console.log(i + " is an odd number.");
}
```