# 9.0: Loops

In this module we'll begin studying loops in C#. **NOTE:** you will run into some topics that you will not see until further modules.

## File Location

1. Right click on the solution you made in the first module.
2. Go to **Add > New Project** and select **Console App (.NET Framework)**.
3. Name it `09_loops`.

## Description

Situations will arise where you need to execute a block of code over and over to collect the right data. Maybe we want to check our database for all users who have been active in the last 3 months. Instead of manually checking this, we want to write loops that will look through the database for us. There are multiple types of loops, and it takes a while to learn to use them. Here we start to introduce them to you with some practice.

## While Loops

While loops execute a block of code as long as the condition you give it is true. Once the condition is false, it will stop. Below is an example:

```csharp
class Program
{
    static void Main(string[] args)
    {
        //1
        int number = 0;
            //2
        while(number <= 100)
        {
            //3
            Console.WriteLine(number);
            number = number + 5;
            //4
        }
        //5
        Console.ReadLine();
    }
}
```

> *While the given number is less than or equal to 100, complete the function.*

1. We declare a variable and initialize its value to 0.
2. Using the `while` keyword, we check to see if the number is less than 100. If that is true, we execute the code inside the curly braces. &#x20;
3. We print the number. Then, we add 5 to the number. The number will now be valued at 5.&#x20;
4. We go back to the top of the loop. Since the number is now 5 and less than 100, it will execute again.&#x20;
5. The loop will continue adding 5 to the variable. Once it hits 105, we stop the loop. &#x20;

## For Loops

For loops are probably the most common loop in programming. Let's take a look:

```csharp
int number = 100;

//1         //2          //3
for(int i = 1; i <= number; i++)
{
    //4
    Console.WriteLine(i);
}
//5
```

## Analysis

There are three expressions in the for loop syntax. 1. The first expression is a variable with initialization. We use for loop syntax and declare a variable called `i`. This provides an index of where the loop will start. Here we tell the loop to start at 1.\
2\. The second expression is a conditional expression. We tell the loop that as long as the index is less than or equal to `number`, which we state is 100, to keep looping. The loop will keep going as long as this expression resolves to `true`. 3. We increment the variable `i` by 1 each time we go through the loop. 4. We print the value of `i`. 5. After i becomes greater than the `number` variable(101), we leave the loop.

## Infinite Looping

We could also decrement here by doing `i--`, but we would get an infinite loop. `i` would always be less than 100 so it would loop forever: 1, 0, -1, -2, etc.

## Other Loops

There are a couple of other types of loops within C#, but we'll start here. When you're ready, move to the next module to work on some [loop challenges.](https://eleven-fifty-academy.gitbook.io/dotnet-100-prework-gitbook/part-3-c-fundamentals/9.0-loops/9.0a-loop-challenges)