What computer programs do

First of all, it's useful to have a conceptual idea of what a computer program is and what it does. There are two main aspects to a computer program:

A program is a series of instructions or steps for the computer to carry out.
Each step ultimately involves manipulating some piece of information or data.

In a general sense, a computer program is just a list of step-by-step instructions that you give to the computer, which it performs one by one. Each individual instruction is known as a statement. As you'll see throughout this manual, in ActionScript, each statement is written with a semicolon at the end.

In essence, all that a given instruction in a program does is manipulate some bit of data that's stored in the computer's memory. In a simple case, you might instruct the computer to add two numbers and store the result in its memory. In a more complex case, imagine there is a rectangle drawn on the screen, and you want to write a program to move it somewhere else on the screen. The computer is keeping track of certain information about the rectangle--the x, y coordinates where it's located, how wide and tall it is, what color it is, and so forth. Each of those bits of information is stored somewhere in the computer's memory. A program to move the rectangle to a different location would have steps like "change the x coordinate to 200; change the y coordinate to 150" (in other words, specifying new values to be used for the x and y coordinates). Of course, the computer does something with this data to actually turn those numbers into the image that appears on the computer screen; but for the level of detail we're interested in, it's enough to know that the process of "moving a rectangle on the screen" really just involves changing bits of data in the computer's memory.

Flash CS3

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