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Data Types

Objectives

Having read this section you should be able to:

  1. declare (name) a local variable as being one of C's five data types
  2. initialise local variables
  3. perform simple arithmetic using local variables

Now we have to start looking into the details of the C language. How easy you find the rest of this section will depend on whether you have ever programmed before - no matter what the language was. There are a great many ideas common to programming in any language and C is no exception to this rule.

So if you haven't programmed before, you need to take the rest of this section slowly and keep going over it until it makes sense. If, on the other hand, you have programmed before you'll be wondering what all the fuss is about It's a lot like being able to ride a bike!

The first thing you need to know is that you can create variables to store values in. A variable is just a named area of storage that can hold a single value (numeric or character). C is very fussy about how you create variables and what you store in them. It demands that you declare the name of each variable that you are going to use and its type, or class, before you actually try to do anything with it.

In this section we are only going to be discussing local variables. These are variables that are used within the current program unit (or function) in a later section we will looking at global variables - variables that are available to all the program's functions.

There are five basic data types associated with variables:

  1. int - integer: a whole number.
  2. float - floating point value: ie a number with a fractional part.
  3. double - a double-precision floating point value.
  4. char - a single character.
  5. void - valueless special purpose type which we will examine closely in later sections.

One of the confusing things about the C language is that the range of values and the amount of storage that each of these types takes is not defined. This is because in each case the 'natural' choice is made for each type of machine. You can call variables what you like, although it helps if you give them sensible names that give you a hint of what they're being used for - names like sum, total, average and so on. If you are translating a formula then use variable names that reflect the elements used in the formula. For example, 2(r (that should read as "2 pi r" but that depends upon how your browser has been set-up) would give local variables names of pi and r. Remember, C programmers tend to prefer short names!

Note:all C's variables must begin with a letter or a "_" (underscore) character.