Hiding Details

Functions can also be used to take the details out of main(), or to hide details from other programmers who use them.

What is the point?

Improve program readability

To make our main program simpler and easier to read. For instance, we could call a function named PrintGreeting( ) and assume that it will do just that. We have now managed to remove many lines of code that just clutter the main program. Here is an example


/*******************************************************************
* PrintGreeting( ) 
* prints an initial message when the program starts.
*
* INPUTS: none
* OUTPUT: none
* SIDE EFFECTS: prints to stdout
*******************************************************************/

void PrintGreeting( void )
{
    printf("\n\n");
    printf("*************************************\n");
    printf("*Hello.                             *\n");
    printf("*This program finds the surface area*\n");
    printf("*and volume of a sphere.            *\n");
    printf("*************************************\n\n");
}

Information hiding promotes modularity

In order for other programmers to make use of functions we've written, it is sufficient for them to know what the function does, what arguments it takes and its return type. They do not need to know how we decided to write the code within the function definition.
This means that we are free to change or improve the working of our function without effecting the other programmers who are using it. (Assuming we don't break it!)
Such "information hiding" is a key to building modular programs, especially among a group of programmers.
- Some advanced programming languages, such as Eiffel, have developed this into a powerful paradigm -- programming by contract.

The functional approach

This only works if we are careful to avoid (as much as possible)

Having our functions perform unexpected side effects
Depend on variables or constants not passed as arguments

We'll see more of these ideas later