Definitions

There are several new terms introduced in this chapter. Be particularly careful since some of these are interchangeable: for example, most programmers consider the terms line, code, command and statement to mean just about the same thing – that is, one line of programming instruction. Normally, however, code refers to one or more instructions.

In general use, the following terms can often be used interchangeably.

• Flow: The order of execution of statements. The flow may be designed to repeat or skip some statements
• Execution: the process of carrying out the instruction in a statement

And remember, there are two types of statements:

• Action statements: Statements that perform an activity, such as the creation of a part of a page, a change to a variable, a redirection to another page, or changing a setting on the server.
• Control statements: Statements that give instructions on which statements to execute, and in what order.

These statements can be organized into larger groups:

• Code structures: Several lines of code that work together to achieve a task. For example, five lines of code may work to put data into a table.
• Control structures: Since controlling flow frequently requires several control statements, we call a set of statements that govern the order of execution a control structure.