Introduction to Arrays

After this lesson you can

• Explain what an array is and when to use one

Key takeaways

• An array keeps many related values together under one name, each in its own numbered spot.
• An array's size is fixed when you make it. For more values, you need a bigger array.
• Every value in an array has the same type: an int[] holds only whole numbers, a string[] only text.
• Use an array instead of separate variables such as score1 and score2: the values travel together, and Length counts them.

So far, every variable you've made holds one value: one score, one price, one name. But real programs work with groups: a team's scores for every game, the prices in a shopping cart, the names in a class. An array lets you keep many related values together as one group, under one name.

An egg carton

Think about buying eggs. Even if you buy them one at a time at a farmers' market, you'd still put them in a container to carry them home.

Each egg is like a variable. Just as you want to keep your eggs together, you'll often want to keep values together. An egg carton is like an array: a container made for holding eggs, in numbered spots.

Fixed in size

An array has a fixed size. If you have a 6-egg carton, you can't stretch it to fit 12 eggs. You'd need a bigger carton, and you'd move the 6 eggs into it.

Arrays work the same way: you choose the size when you make one, and it never changes.

One type of thing

An array holds values of one type. You wouldn't put a dozen eggs in a 12-pack box made for soda cans. In the same way, an array of string values holds only text, and an array of int values holds only whole numbers.

Why use an array?

Compare five separate variables with one array:

int score1 = 80;
int score2 = 85;
int score3 = 90;
int score4 = 75;
int score5 = 95;

int[] scores = { 80, 85, 90, 75, 95 };
Console.WriteLine("Games played: " + scores.Length);

Games played: 5

With separate variables, adding a sixth game means a new variable and new code everywhere you use them. With an array, the values travel together: you can pass all of them to a method at once, count them with Length, and, as you'll see in this chapter, visit every one of them with a loop.

Check yourself

1 question to try on the lesson page.

So what

Most interesting data comes in groups. An array is the simplest way to keep a group together: one name, one type, a fixed number of numbered spots.

Key terms

• Array

Cheat sheets

• Introduction to Arrays