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C is a powerful and compact computer language that allows you to write programs that specify exactly what you want your computer to do. You’re in charge: you create a program, which is just a set of instructions, and your computer will follow them.

By now you’re probably eager to create programs that allow your computer to really interact with the outside world. You don’t just want programs that work as glorified typewriters, displaying fixed information that you included in the program code, and indeed there’s a whole world of programming that goes beyond that.

In Chapter 2 you learned how to do calculations in your programs. In this chapter, you’ll take great leaps forward in the range of programs you can write and the flexibility you can build into them. You’ll add one of the most powerful programming tools to your inventory: the ability to compare the values of expressions and, based on the outcome, choose to execute one set of statements or another.

In the last chapter you learned how to compare items and base your decisions on the result. You were able to choose how the computer reacted based on the input to a program. In this chapter, you’ll learn how you can repeat a block of statements until some condition is met. This is called a .

You’ll often need to store many data values of a particular kind in your programs. For example, if you were writing a program to track the performance of a basketball team, then you might want to store the scores for a season of games and the scores for individual players. You could then output the scores for a particular player over the season or work out an ongoing average as the season progresses. Armed with what you’ve learned so far, you could write a program that does this using a different variable for each score. However, if there are a lot of games in the season, this will be rather tedious because you’ll need as many variables for each player as there are games. All your basketball scores are really the same kind of thing. The values are different, but they’re all basketball scores. Ideally, you would want to group these values together under a single name—perhaps the name of the player—so that you wouldn’t have to define separate variables for each item of data.

In the last chapter you were introduced to arrays and you saw how using arrays of numerical values could make many programming tasks much easier. In this chapter you’ll extend your knowledge of arrays by exploring how you can use arrays of characters. You’ll frequently have a need to work with a text string as a single entity. As you’ll see, C doesn’t provide you with a string data type as some other languages do. Instead, C uses an array of elements of type char to store a string.

You had a glimpse of pointers in the last chapter and just a small hint at what you can use them for. Here, you’ll delve a lot deeper into the subject of pointers and see what else you can do with them.

I mentioned in Chapter 1 that breaking up a program into reasonably self-contained units is basic to the development of any program of a practical nature. When confronted with a big task, the most sensible thing to do is break it up into manageable chunks. You can then deal with each small chunk fairly easily and be reasonably sure that you’ve done it properly. If you design the chunks of code carefully, you may be able to reuse some of them in other programs.

Now that you’ve completed Chapter 8, you have a good grounding in the essentials of creating and using functions. In this chapter you’ll build on that foundation by exploring how functions can be used and manipulated; in particular, you’ll investigate how you can access a function through a pointer. You’ll also be working with some more flexible methods of communicating between functions.

In this chapter you’re going to look in more detail at input from the keyboard, output to the screen, and output to a printer. The good news is that everything in this chapter is fairly easy, although there may be moments when you feel it’s all becoming a bit of a memory test. Treat this as a breather from the last two chapters. After all, you don’t have to memorize everything you see here; you can always come back to it when you need it.