From David Bolton,
Your Guide to C / C++ / C#.
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In C there are two types of numbers. Ints and floats. There are also variants of these types that hold bigger numbers, or only unsigned numbers but they are still ints or floats.

An int is a whole number like 47 without a decimal point. You can't have 4.5 babies or loop 32.9 times. You can have $25.76 if you use a float. So when you create your program, you must decide which type to use.

Why Decide?

Why not just store everything as floats, as some scripting languages do? Because it's inefficient, floats take up more memory and are generally slower than ints. Also you cannot easily compare two floats to see if they are equal like you can with ints.

To manipulate numbers you have to store them in memory. Because the value can be easily changed, it's called a variable. The compiler that reads your program and converts it into machine code needs to know what type it is, ie whether it's an int or a float, so before your program uses a variable, you must declare it.

Here's an example.

int Counter =0;
float BasicSalary;

You'll notice that the Counter variable is set to 0. This is an optional initialization. It's a very good practice to initialize variables. If you don't initialize and then use them in code without having set a value then you will end up with a random value that will most likely 'break' your code. The value will be whatever was in memory when the program was loaded.

On the next page : Learn more about ints.