Overview                                                                                                                                                                    
The following is a description of some of the basic data types native to C as well as a quick introduction to some of the more complex data types that will be covered in later sections. I won’t cover all basic data types and I won’t cover all of their qualifiers either, if you’re interested in a complete introduction see a text. All examples assume a 32 bit Windows OS ( NT4, 98, 2000).

Numbers                                                                                                                                                                    
The three most common number types are:

A keyword commonly used with the int type is: unsigned. This means that all numbers assigned to the variable will be positive thus increasing the range of positive numbers that the variable can hold ( i.e. the range is all on the positive side of 0 rather than being split down the middle by 0 ). See Ranges below.

int
An integer is a whole number, that is no decimal. By default an int is assumed to be “signed” and can thus be a positive or negative number. If defined as “unsigned” then the numbers can only be positive.

float
A float is a number that can contain decimal information. A float has a precision of 7 digits, and the decimal counts as one of those digits. Floats are used when you need more precision than an int allows.

double
A double is a float that has a greater precision, 15 digits. The greater precision is at the expense of memory as a double is double the size of a float. Usually you can get away with floats, be careful with doubles… memory adds up quickly.

There are other qualifiers such as small, short, long and hyper; see a text for more info.

Characters                                                                                                                                                               
a char is text
If you are unfamiliar with C entirely then you will no doubt find the way it handles “strings” rather cumbersome. I don’t really blame you if you do, while I can see how it makes sense and is quite powerful it is at the same time confusing to beginners. A character is a single letter or symbol, or simply: text. A string is a “string” of characters, or: words and sentences. There is no string type in C, rather we use an array of characters to make up word and sentences ( or text files ). We’ll see how this is done later in Strings.

letters and symbols are represented by ASCII codes
Ok, read this next part carefully because it will be important later on. A char is really an integer. Bear with me on this. C uses a code to represent each letter and symbol called an ASCII code. The codes for the uppercase letters range from 65 to 90, and lowercase ranges from 98 to 115. So if you wrote the following line of code:

charmychar = 65;

it would be equivalent to the following line:

charmychar = ‘A’;

Note that we use single quotes around characters ( later we will see that we use double quotes around strings, so keep them straight ). The fist line doesn’t have quotes around the number 65 so we are assigning the value of 65 directly to the char, that is we are setting it’s ASCII code to 65 (which corresponds to the letter A). In the second line we use ‘A’ instead which gets interpreted as the number 65.

chars as colors?
Under ordinary circumstances you wouldn’t need to concern yourself with this, however graphics programming has a rather peculiar use for chars that you might not expect. When representing the value of a color component (i.e. red, green or blue) the data type of choice is an unsigned char. The reason for this is that a char is 1 byte which gives it a range of 0 to 255 when it is unsigned. The standard color schemes used by most 3D apps use 256 levels for each color component giving 256*256*256 (or 16,777,216) color combinations. A char is used for memory considerations, using an int which is 4 times as large as a char would greatly increase the size of images and RAM needed for 3D work. Just keep that in mind later on, a char is basically a 1 byte int that can be interpreted as a character.

Arrays                                                                                                                                                                        

an array is a collection of items of similar type
Arrays are not really a data type but rather an extension to all data types ( more or less ). In other words you can have an array of integers or an array of characters. An array is just a collection of items of similar type. To get us prepared for strings later on we’ll look at an example of an array of characters.

A variable must be declared as an array at the time you declare the variable. It is done by appending a [] to the variable name. Inside the square brackets you place a number to indicate the size of the array. The size indicates the number of items are in the array ( not the number of bytes ). So to create an array of 10 characters we write the following:

charmystring[10];

elements in an array are accessed by index
You access each element in the array with an “index”. The index starts at 0 and then goes up to the total number of elements minus 1. This is one of the things that gives beginners a lot of trouble. The number of elements in an array is often called ‘n’ in most programming notation (actually n is commonly used to represent “the number of” something where that number can vary). So an array’s indices for an array of size n range from 0 to n-1. In the example above the last element in the array is mystring[9].

To set the value of an element you simply specify the index number you want to change:

mystring[5] = ‘j’;

initializing an array at declaration
Most texts on C will take you through the grueling task of creating strings by assigning each letter individually. While that may be an important lesson we’ll skip ahead a bit. An array’s size need not be set explicitly, rather you can initialize the variable at declaration which will implicitly set the size of the array. So the following is perfectly legal:

charmystring[] = “Hello World”;

Here an array of chars will be created with a size of 12 chars. Yes 12, I’ll explain why the extra one when we get to Strings. You can only assign a value to an array like this at declaration, after that you must access each index individually ( again, not entirely true but close enough ).

So an array of ints is just as easy:

int  my_int_array[10];    // creates an array of 10 ints

int  my_int_array[] = { 0, 1, 2, 3, 8, 5, 6, 7, 8, 9};
                           // also creates an array of 10 ints
                           // but also initializes their values

Using the second definition from above my_int_array[4] would equal 8.

Since you are no doubt familiar with arrays in whatever scripting language you are used to I’ll leave the discussion at that. That should be enough to get you started with them.

Pointers                                                                                                                                                                    
We will discuss pointers in depth in the next section. For know just know that they allow you to use a variable to “reference” some other data. In other words if I have an array of 1000 ints, I can create a variable that is a pointer to an array of ints that will reference that large array. Why you would want to do that will be discussed later, be patient.

Ranges                                                                                                                                                                
This table shows the size of each data type and the range of possible values and precision of each type. Don’t worry too much about memorizing it, just remember where it is when you need to come back to it.