Functions

Here is the basic structure of a C function:

return_data_type function_name (data_type variable_name...)

{

< statements >

return value;

}

 

• The data_type and return_data type can be any defined type in C. These include int (integer values), float (floating point values, like reals but not exactly: see variables), char (character values), and for functions: void, which is a null type. If a function is declared as type void, there is no return value.
  
• function_name can be any name you make up. However, the same restrictions that apply to variable names apply to function names. They must start with an underscore: '_' or a letter and be followed by zero or more alpha-numeric characters and/or underscores. In C, variable and function names are case-sensitive. That means that 'my_var' is different than 'My_var.'
  In general, you should try to give meaningful names to your functions and variables, names that indicate their purpose. For example, if you have a variable which is the running total of some addition operations, call it 'sum' rather than 'x.'
  
• Functions are executed only when they are 'called.' A function call looks like this:

  function_name (value, value, etc...);

  (value, value, etc.) indicates values that are 'passed into' the function. They must match both in number and type the list of 'parameters' in the function declaration.
  When a function is called, the values are ' bound' to the variables of the function.
  

• See the page on variable scope for more information about functions.