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While Loops

Name: While Loops
Uploaded: 2016-05-10T13:51:55-04:00
Duration: 235 s
Description: One way to work with every object in an array is with a while loop.

3:55 with Jeremy McLain

One way to work with every object in an array is with a while loop.

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While Loops

The difference between ++ on the left side of a variable versus ++ on the right side of a variable - Pay attention to the code example for a demonstration of how these two are different.

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[MUSIC] 0:00

Now that we finished up the Invader class, let's move on to the Tower class. 0:04

So far the Tower class is completely empty, let's fill it out. 0:09

First each Tower will need to have a location on the map, so 0:13

let's add a field for that. 0:16

Nothing outside the class needs to know the location of the Towers, 0:18

so we won't create a MapLocation property. 0:21

This will just be a field, because each tower needs to have a location on the map, 0:25

it should be a parameter in the constructor. 0:30

And we'll need to use it to set the location field. 0:32

Now most tower defense games don't allow placing towers on the path. 0:43

We could add some validation here to ensure the towers can't be 0:48

placed on paths. 0:51

In fact, you know what? 0:53

You already saw an example of this validation pattern when we created 0:54

the MapLocation class. 0:57

I'll leave that as a challenge for you to do on your own. 0:59

Now we need to think about what other behaviors and attribute Towers will need. 1:03

One behavior I can think of is the ability to shoot at invaders. 1:08

Let's create a method called FireOnInvaders. 1:13

This Method will go through all of the Invaders on the map and 1:16

check to see if they are in range. 1:19

If they are, the Tower will shoot at them and decrease their health. 1:21

This method will need to have access to all the Invaders on the map. 1:26

So we'll pass them in as an array. 1:31

Now we'll need to determine which invaders are in range. 1:33

To do that we'll need to look at each invader in the array. 1:37

For that we'll need a loop. 1:41

Let's look at how we would use a while loop for this. 1:44

If you're unfamiliar with while loops check out the teacher's notes for 1:47

a link to a Treehouse course that covers them. 1:50

We'll need to loop through each index in the array. 1:54

So we'll need a variable to keep track of where we are in the array. 1:57

Let's create an integer variable called index here and initialize it to zero. 2:01

Now let's create a while loop that will stop when it gets to the end of the array. 2:07

To do that, we'll check if the index is less than the length of the array. 2:11

The last index in an array is always one less than the length of 2:19

the array because we start counting at zero. 2:22

If index equals the length of the array, 2:25

then we know that it's time to exit the loop. 2:28

Now we can use the index variable to index into the array. 2:31

We'll assign it to a variable so we don't have to index into the array 2:35

every time we want to reference this specific Invader. 2:38

Now that we have an Invader from the array, 2:42

we can do whatever we want with it here. 2:45

Finally we'll need to add one to the index variable so 2:47

that the next time through the loop we're getting the next invader in the array. 2:50

This way, we can do something with each of the items in the array. 2:54

This is called incrementing the index variable by one. 2:59

Incrementing is so common that there is some syntactic sugar for it. 3:03

Instead of saying index plus equals one, we can just type index++. 3:07

This is shorthand for adding one to the index variable. 3:13

Sometimes you may see the ++ at the start of the variable name. 3:17

There's a very subtle difference between these two forms. 3:21

I've included a description of these differences in the teacher's notes. 3:24

In most case, you want to put the ++ on the right side of the variable. 3:28

Our while loop as it's written will loop through each item in the array 3:32

one at a time. 3:36

This allows us to do something with each item by adding some code right here where 3:38

C# Objects

While Loops

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