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Next: Functions with no parameters Up: Introduction to C++ Programming Previous: Exercises

Introduction to User-defined functions in C++

C++ allows programmers to define their own functions. For example the following is a definition of a function which given the co-ordinates of a point (x,y) will return its distance from the origin.

float distance(float x, float y)
      // Returns the distance of (x, y) from origin
   {
    float dist;  //local variable
    dist = sqrt(x * x + y * y);
    return dist;
   }

Download program.

This function has two input parameters, real values x and y, and returns the distance of the point (x,y) from the origin. In the function a local variable dist is used to temporarily hold the calculated value inside the function.

The general form of a function definition in C++ is as follows:

function-type function-name( parameter-list )
{
local-definitions;
function-implementation;
}

If the function returns a value then the type of that value must be specified in function-type. For the moment this could be int, float or char. If the function does not return a value then the function-type must be void.
The function-name follows the same rules of composition as identifiers.
The parameter-list lists the formal parameters of the function together with their types.
The local-definitions are definitions of variables that are used in the function-implementation. These variables have no meaning outside the function.
The function-implementation consists of C++ executable statements that implement the effect of the function.

Subsections

Next: Functions with no parameters Up: Introduction to C++ Programming Previous: Exercises