<< Chapter < Page Chapter >> Page >
Most computer programs that solve real-world problems are much larger than the programs in the first few chapters. Experience has shown that the best way to develop and maintain a large program is to construct it from smaller pieces or program units each, of which is more manageable than the original program. Generally, user-defined program units are called subprograms. This technique is called divide-and-conquer. This chapter deals with the method of declaration of the user-defined function and its use in C++. Besides, this chapter also covers pointer data type which is one of the strength of the C++ language.

Function and parameter declarations

In C++ all subprograms are referred to as functions . A function allows you to treat a related group of C++ statements as a single unit. The programmer can write functions to define specific tasks that could be used at many points in a program.

Functions allow the programmer to modulize a program. All variables declared in function definitions are local variables – they are known only in the function in which they are defined. Most functions have a list of parameters that provide the means for communicating information between functions.

There are several motivations for dividing a program into functions. The divide-and-conquer approach makes program development more manageable. Another motivation is software reusability – using existing functions as building blocks to create new programs. Software reusability is a major factor in object-oriented programming. With good function naming and definition, programs can be created from standardized functions that accomplish specific tasks. A third motivation is to avoid repeating code in a program. Packing code as a function allows the code to be executed from several location in a program simply by calling the function.

Defining a function

The lines that compose a function within a C++ program are called a function definition. The syntax for defining a function is

data_type name_of_function (parameters){

statements;

}

A function definition consists of four parts:

- A reserved word indicating the return data type of the function’s return value.

- The function name

- Any parameters required by the function, contained within parentheses.

- The function’s statements enclosed in curly braces { }.

Example: The following function determines the largest integer among three parameters passed to it.

int maximum( int x, int y, int z )

{

int max = x;

if ( y>max )

max = y;

if ( z>max )

max = z;

return max;

}

You designate a data type for function since it is common to return a value from a function after it executes.

General format of a function is described below.

General format of a function

Variable names that will be used in the function header line are called formal parameters.

How to call functions

To execute a function, you must invoke, or call, it from the main () function.

The values or variables that you place within the parentheses of a function call statement are called arguments or actual parameters.

Get Jobilize Job Search Mobile App in your pocket Now!

Get it on Google Play Download on the App Store Now




Source:  OpenStax, Programming fundamentals in c++. OpenStax CNX. Jul 29, 2009 Download for free at http://cnx.org/content/col10788/1.1
Google Play and the Google Play logo are trademarks of Google Inc.

Notification Switch

Would you like to follow the 'Programming fundamentals in c++' conversation and receive update notifications?

Ask