1. User Defined Functions
Chapter 6

2. Chapter Topics Standard (Predefined) Functions User-Defined Functions
Value-Returning Functions
The return Statement
Function Prototype
Flow of Execution

3. Top-Down Structured Design with Functions
Recall two types of functions
Value returning function
computes a single value
returns value to calling code
uses return command
Void function (procedure)
called as a statement
executes some task
This chapter focuses on the value returning function

4. Advantages of Using Functions
To help make the program more understandable
To modularize the tasks of the program
building blocks of the program
Write a module once
those lines of source code are called multiple times in the program

5. Advantages of Using Functions
While working on one function, you can focus on just that part of the program
construct it,
debug it,
perfect it.
5. Different people can work on different functions simultaneously.
6. If a function is needed in more than one place in a program, or in different programs, you can write it once and use it many times

6. Standard (Predefined) Functions
Part of the C++ language
Provided in function libraries
Examples: abs(x), sin(x), log(x), pow( x, n)
These functions will return a value
To be printed cout << sin (x);
To be assigned y = pow (3, 4.5);
To be used in an expression * sqr(r)
Make sure to use the required #include file

7. Predefined Functions
View sample program

8. Value-Returning Functions
All the properties together make up the definition of the function
Information provided by the heading of the function
For the compiler to use a function you have written, it must know when it finds that function call in your source code …
1. The name of the function
2. The number of parameters, if any
3. The data type of each parameter
4. Data type of the value returned by the function
5. The code required to do the calculation
Information provided in the body of the function

9. Value-Returning Functions
Consider a function for the area of a circle: double circleArea (double radius) { return * radius * radius; }
Note the
Heading (type, name, parameters)
The body
The return statement

10. Parameters Function definition syntax:
functionType functionName (formal parameter list) {
statements }
Call (invocation of the function) cout << "Enter radius for circle area -> "; cin >> radius; area = circleArea (radius);
Parameters in the declaration : formal parameters
Parameters in the call: actual parameters

11. The return Statement
A value returning statement must have a return statement
Else a warning from the compiler
Also the function will actually return a "garbage" value
Syntax: return expression;
View example

12. Function Prototype
Recall that the compiler must know certain things about your function
When it finds a function call in your source code
Must know information in heading
Your program must have at least the heading of a function before it is invoked
Usually listed before function main ( )
View example

13. Alternative to Prototype
Also possible to place whole function definition before main ()
This is a requirement in some languages (Pascal)
Either is acceptable in this class
There may be a standard required of programmers within a particular organization
View Example

14. Flow of Control
First statement executed in any program is the first statement in the function main( )
When another function called
logical control passed to first statement in that function’s body
program proceeds through sequence of statements within the function
When last statement of function executed
control returns to where function was called
control given to next command after the call

15. Flow of Control
void main ( ) { print_summary (rpt_total); revenue = rpt_total * ; } void print_summary (int total) { cout << }
- first statement of main - function call, jumps to first statement of that function - proceeds through function - returns to next statement after call