This document discusses user-defined functions in C++. It covers defining functions with return types and parameters, using return statements, function prototypes, and the flow of execution when a function is called. Functions help make programs more modular and understandable by breaking tasks into reusable blocks of code. Defining functions properly allows the compiler to understand how to execute function calls within a program.

1. 1
User Defined Functions

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

3. 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

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

5. 5
Advantages of Using Functions
1. 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. 6
Standard (Predefined) Functions
 Predefined functions
 Part of the C++ language
 Provided in function libraries
 Examples:
abs(x), sin(x), log(x), pow( x, n)abs(x), sin(x), log(x), pow( x, n)
 These functions will return a value
 To be printed cout << sin (x);cout << sin (x);
 To be assigned y = pow (3, 4.5);y = pow (3, 4.5);
 To be used in an expression 3.14 * sqr(r)3.14 * sqr(r)
Make sure to use
the required
#include#include file

7. 7
Predefined Functions
View
sample
progra
m

8. 8
Value-Returning Functions
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
by the heading of the
function
Information provided in
the body of the function
All the properties
together make up
the definition of the
function

9. 9
Value-Returning Functions
 Consider a function for the area of a circle:
double circleArea (double radius)double circleArea (double radius)
{{
return 3.14159 * radius *return 3.14159 * radius *
radius;radius;
}}
 Note the
 Heading (type, name, parameters)
 The body
 The return statement

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

11. 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;return expression;
 View example

12. 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 ( )main ( )
 View example

13. 13
Alternative to Prototype
 Also possible to place whole function
definition before main ()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. 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. 15
Flow of Control
void main ( )
{ . . .
print_summary (rpt_total);
revenue = rpt_total * .72675;
. . .
}
void print_summary (int total)
{ . . .
cout << . . .
}
void main ( )
{ . . .
print_summary (rpt_total);
revenue = rpt_total * .72675;
. . .
}
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
- first statement of main
- function call, jumps to first statement
of that function
- proceeds through function
- returns to next statement after call