power point presentation on object oriented programming functions concepts
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The document discusses C++ functions. It covers the following key points in 3 sentences:
Standard functions that are included with C++ like math functions are discussed as well as how to define user-defined functions. User-defined functions are defined with a function header, parameters, and body. Functions can share data through parameters, either by value or by reference, and variables can have local or global scope.
1 of 70
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power point presentation on object oriented programming functions concepts
2. 2
Agenda
What is a function?
Types of C++
functions:
Standard functions
User-defined functions
C++ function structure
Function signature
Function body
Declaring and
Implementing C++
functions
Sharing data among
functions through
function parameters
Value parameters
Reference parameters
Const reference
parameters
Scope of variables
Local Variables
Global variable
3. 3
Functions and subprograms
The Top-down design appeoach is based on dividing the
main problem into smaller tasks which may be divided
into simpler tasks, then implementing each simple task
by a subprogram or a function
A C++ function or a subprogram is simply a chunk of
C++ code that has
A descriptive function name, e.g.
computeTaxes to compute the taxes for an employee
isPrime to check whether or not a number is a prime number
A returning value
The computeTaxes function may return with a double number
representing the amount of taxes
The isPrime function may return with a Boolean value (true or false)
4. 4
C++ Standard Functions
C++ language is shipped with a lot of functions
which are known as standard functions
These standard functions are groups in different
libraries which can be included in the C++
program, e.g.
Math functions are declared in <math.h> library
Character-manipulation functions are declared in
<ctype.h> library
C++ is shipped with more than 100 standard libraries,
some of them are very popular such as <iostream.h>
and <stdlib.h>, others are very specific to certain
hardware platform, e.g. <limits.h> and <largeInt.h>
5. 5
Example of Using
Standard C++ Math Functions
#include <iostream.h>
#include <math.h>
void main()
{
// Getting a double value
double x;
cout << "Please enter a real number: ";
cin >> x;
// Compute the ceiling and the floor of the real number
cout << "The ceil(" << x << ") = " << ceil(x) << endl;
cout << "The floor(" << x << ") = " << floor(x) << endl;
}
6. 6
Example of Using
Standard C++ Character Functions
#include <iostream.h> // input/output handling
#include <ctype.h> // character type functions
void main()
{
char ch;
cout << "Enter a character: ";
cin >> ch;
cout << "The toupper(" << ch << ") = " << (char) toupper(ch) << endl;
cout << "The tolower(" << ch << ") = " << (char) tolower(ch) << endl;
if (isdigit(ch))
cout << "'" << ch <<"' is a digit!n";
else
cout << "'" << ch <<"' is NOT a digit!n";
}
Explicit casting
7. 7
User-Defined C++ Functions
Although C++ is shipped with a lot of standard
functions, these functions are not enough for all
users, therefore, C++ provides its users with a
way to define their own functions (or user-
defined function)
For example, the <math.h> library does not
include a standard function that allows users to
round a real number to the ith digits, therefore,
we must declare and implement this function
ourselves
8. 8
How to define a C++ Function?
Generally speaking, we define a C++
function in two steps (preferably but not
mandatory)
Step #1 – declare the function signature in
either a header file (.h file) or before the main
function of the program
Step #2 – Implement the function in either an
implementation file (.cpp) or after the main
function
9. 9
What is The Syntactic Structure of
a C++ Function?
A C++ function consists of two parts
The function header, and
The function body
The function header has the following
syntax
<return value> <name> (<parameter list>)
The function body is simply a C++ code
enclosed between { }
10. 10
Example of User-defined
C++ Function
double computeTax(double income)
{
if (income < 5000.0) return 0.0;
double taxes = 0.07 * (income-5000.0);
return taxes;
}
11. 11
double computeTax(double income)
{
if (income < 5000.0) return 0.0;
double taxes = 0.07 * (income-5000.0);
return taxes;
}
Example of User-defined
C++ Function
Function
header
12. 12
Example of User-defined
C++ Function
double computeTax(double income)
{
if (income < 5000.0) return 0.0;
double taxes = 0.07 * (income-5000.0);
return taxes;
}
Function
header
Function
body
13. 13
Function Signature
The function signature is actually similar to
the function header except in two aspects:
The parameters’ names may not be specified
in the function signature
The function signature must be ended by a
semicolon
Example
double computeTaxes(double) ;
Unnamed
Parameter
Semicolon
;
14. 14
Why Do We Need Function
Signature?
For Information Hiding
If you want to create your own library and share it with
your customers without letting them know the
implementation details, you should declare all the
function signatures in a header (.h) file and distribute
the binary code of the implementation file
For Function Abstraction
By only sharing the function signatures, we have the
liberty to change the implementation details from time
to time to
Improve function performance
make the customers focus on the purpose of the function, not
its implementation
15. 15
Example
#include <iostream>
#include <string>
using namespace std;
// Function Signature
double getIncome(string);
double computeTaxes(double);
void printTaxes(double);
void main()
{
// Get the income;
double income = getIncome("Please enter
the employee income: ");
// Compute Taxes
double taxes = computeTaxes(income);
// Print employee taxes
printTaxes(taxes);
}
double computeTaxes(double income)
{
if (income<5000) return 0.0;
return 0.07*(income-5000.0);
}
double getIncome(string prompt)
{
cout << prompt;
double income;
cin >> income;
return income;
}
void printTaxes(double taxes)
{
cout << "The taxes is $" << taxes << endl;
}
16. 16
Building Your Libraries
It is a good practice to build libraries to be
used by you and your customers
In order to build C++ libraries, you should
be familiar with
How to create header files to store function
signatures
How to create implementation files to store
function implementations
How to include the header file to your
program to use your user-defined functions
17. 17
C++ Header Files
The C++ header files must have .h
extension and should have the following
structure
#ifndef compiler directive
#define compiler directive
May include some other header files
All functions signatures with some comments
about their purposes, their inputs, and outputs
#endif compiler directive
18. 18
TaxesRules Header file
#ifndef _TAXES_RULES_
#define _TAXES_RULES_
#include <iostream>
#include <string>
using namespace std;
double getIncome(string);
// purpose -- to get the employee
income
// input -- a string prompt to be
displayed to the user
// output -- a double value
representing the income
double computeTaxes(double);
// purpose -- to compute the taxes for
a given income
// input -- a double value
representing the income
// output -- a double value
representing the taxes
void printTaxes(double);
// purpose -- to display taxes to the
user
// input -- a double value
representing the taxes
// output -- None
#endif
20. 20
Main Program File
#include "TaxesRules.h"
void main()
{
// Get the income;
double income =
getIncome("Please enter the employee income: ");
// Compute Taxes
double taxes = computeTaxes(income);
// Print employee taxes
printTaxes(taxes);
}
21. 21
Inline Functions
Sometimes, we use the keyword inline to define
user-defined functions
Inline functions are very small functions, generally,
one or two lines of code
Inline functions are very fast functions compared to
the functions declared without the inline keyword
Example
inline double degrees( double radian)
{
return radian * 180.0 / 3.1415;
}
22. 22
Example #1
Write a function to test if a number is an
odd number
inline bool odd (int x)
{
return (x % 2 == 1);
}
23. 23
Example #2
Write a function to compute the distance
between two points (x1, y1) and (x2, y2)
Inline double distance (double x1, double y1,
double x2, double y2)
{
return sqrt(pow(x1-x2,2)+pow(y1-y2,2));
}
24. 24
Example #3
Write a function to compute n!
int factorial( int n)
{
int product=1;
for (int i=1; i<=n; i++) product *= i;
return product;
}
25. 25
Example #4
Function Overloading
Write functions to return with the maximum number of
two numbers
inline int max( int x, int y)
{
if (x>y) return x; else return y;
}
inline double max( double x, double y)
{
if (x>y) return x; else return y;
}
An overloaded
function is a
function that is
defined more than
once with different
data types or
different number
of parameters
26. 26
Sharing Data Among
User-Defined Functions
There are two ways to share data
among different functions
Using global variables (very bad practice!)
Passing data through function parameters
Value parameters
Reference parameters
Constant reference parameters
27. 27
C++ Variables
A variable is a place in memory that has
A name or identifier (e.g. income, taxes, etc.)
A data type (e.g. int, double, char, etc.)
A size (number of bytes)
A scope (the part of the program code that can use it)
Global variables – all functions can see it and using it
Local variables – only the function that declare local variables
see and use these variables
A life time (the duration of its existence)
Global variables can live as long as the program is executed
Local variables are lived only when the functions that define
these variables are executed
28. 28
I. Using Global Variables
#include <iostream.h>
int x = 0;
void f1() { x++; }
void f2() { x+=4; f1(); }
void main()
{
f2();
cout << x << endl;
}
29. 29
I. Using Global Variables
#include <iostream.h>
int x = 0;
void f1() { x++; }
void f2() { x+=4; f1(); }
void main()
{
f2();
cout << x << endl;
}
x 0
30. 30
I. Using Global Variables
#include <iostream.h>
int x = 0;
void f1() { x++; }
void f2() { x+=4; f1(); }
void main()
{
f2();
cout << x << endl;
}
x 0
void main()
{
f2();
cout << x << endl ;
}
1
31. 31
I. Using Global Variables
#include <iostream.h>
int x = 0;
void f1() { x++; }
void f2() { x+=4; f1(); }
void main()
{
f2();
cout << x << endl;
}
x 0
void main()
{
f2();
cout << x << endl ;
}
1
void f2()
{
x += 4;
f1();
}
2
4
32. 32
4
5
I. Using Global Variables
#include <iostream.h>
int x = 0;
void f1() { x++; }
void f2() { x+=4; f1(); }
void main()
{
f2();
cout << x << endl;
}
x
void main()
{
f2();
cout << x << endl ;
}
1
void f2()
{
x += 4;
f1();
}
3
void f1()
{
x++;
}
4
33. 33
4
5
I. Using Global Variables
#include <iostream.h>
int x = 0;
void f1() { x++; }
void f2() { x+=4; f1(); }
void main()
{
f2();
cout << x << endl;
}
x
void main()
{
f2();
cout << x << endl;
}
1
void f2()
{
x += 4;
f1();
}
3
void f1()
{
x++;
}
5
34. 34
4
5
I. Using Global Variables
#include <iostream.h>
int x = 0;
void f1() { x++; }
void f2() { x+=4; f1(); }
void main()
{
f2();
cout << x << endl;
}
x
void main()
{
f2();
cout << x << endl;
}
1
void f2()
{
x += 4;
f1();
}
6
35. 35
4
5
I. Using Global Variables
#include <iostream.h>
int x = 0;
void f1() { x++; }
void f2() { x+=4; f1(); }
void main()
{
f2();
cout << x << endl;
}
x
void main()
{
f2();
cout << x << endl;
}
7
36. 36
4
5
I. Using Global Variables
#include <iostream.h>
int x = 0;
void f1() { x++; }
void f2() { x+=4; f1(); }
void main()
{
f2();
cout << x << endl;
}
x
void main()
{
f2();
cout << x << endl;
}
8
37. 37
I. Using Global Variables
#include <iostream.h>
int x = 0;
void f1() { x++; }
void f2() { x+=4; f1(); }
void main()
{
f2();
cout << x << endl;
}
38. 38
What Happens When We Use
Inline Keyword?
#include <iostream.h>
int x = 0;
Inline void f1() { x++; }
Inline void f2() { x+=4; f1();}
void main()
{
f2();
cout << x << endl;
}
39. 39
What Happens When We Use
Inline Keyword?
#include <iostream.h>
int x = 0;
Inline void f1() { x++; }
Inline void f2() { x+=4; f1();}
void main()
{
f2();
cout << x << endl;
}
0
x
void main()
{
x+=4;
x++;
cout << x << endl;
}
1
The inline keyword
instructs the compiler
to replace the function
call with the function
body!
40. 40
What Happens When We Use
Inline Keyword?
#include <iostream.h>
int x = 0;
Inline void f1() { x++; }
Inline void f2() { x+=4; f1();}
void main()
{
f2();
cout << x << endl;
}
4
x
void main()
{
x+=4;
x++;
cout << x << endl;
}
2
41. 41
What Happens When We Use
Inline Keyword?
#include <iostream.h>
int x = 0;
Inline void f1() { x++; }
Inline void f2() { x+=4; f1();}
void main()
{
f2();
cout << x << endl;
}
5
x
void main()
{
x+=4;
x++;
cout << x << endl;
}
3
42. 42
What Happens When We Use
Inline Keyword?
#include <iostream.h>
int x = 0;
Inline void f1() { x++; }
Inline void f2() { x+=4; f1();}
void main()
{
f2();
cout << x << endl;
}
5
x
void main()
{
x+=4;
x++;
cout << x << endl;
}
4
43. 43
What Happens When We Use
Inline Keyword?
#include <iostream.h>
int x = 0;
Inline void f1() { x++; }
Inline void f2() { x+=4; f1();}
void main()
{
f2();
cout << x << endl;
}
44. 44
What is Bad About Using
Global Vairables?
Not safe!
If two or more programmers are working together in a
program, one of them may change the value stored in
the global variable without telling the others who may
depend in their calculation on the old stored value!
Against The Principle of Information Hiding!
Exposing the global variables to all functions is
against the principle of information hiding since this
gives all functions the freedom to change the values
stored in the global variables at any time (unsafe!)
45. 45
Local Variables
Local variables are declared inside the function
body and exist as long as the function is running
and destroyed when the function exit
You have to initialize the local variable before
using it
If a function defines a local variable and there
was a global variable with the same name, the
function uses its local variable instead of using
the global variable
46. 46
Example of Defining and Using
Global and Local Variables
#include <iostream.h>
int x; // Global variable
Void fun(); // function signature
void main()
{
x = 4;
fun();
cout << x << endl;
}
void fun()
{
int x = 10; // Local variable
cout << x << endl;
}
47. 47
Example of Defining and Using
Global and Local Variables
#include <iostream.h>
int x; // Global variable
Void fun(); // function signature
void main()
{
x = 4;
fun();
cout << x << endl;
}
void fun()
{
int x = 10; // Local variable
cout << x << endl;
}
x 0
Global variables are
automatically initialized to 0
48. 48
Example of Defining and Using
Global and Local Variables
#include <iostream.h>
int x; // Global variable
Void fun(); // function signature
void main()
{
x = 4;
fun();
cout << x << endl;
}
void fun()
{
int x = 10; // Local variable
cout << x << endl;
}
x 0
void main()
{
x = 4;
fun();
cout << x << endl;
}
1
49. 49
Example of Defining and Using
Global and Local Variables
#include <iostream.h>
int x; // Global variable
Void fun(); // function signature
void main()
{
x = 4;
fun();
cout << x << endl;
}
void fun()
{
int x = 10; // Local variable
cout << x << endl;
}
x 4
void main()
{
x = 4;
fun();
cout << x << endl;
}
2
void fun()
{
int x = 10;
cout << x << endl;
}
x ????
3
50. 50
Example of Defining and Using
Global and Local Variables
#include <iostream.h>
int x; // Global variable
Void fun(); // function signature
void main()
{
x = 4;
fun();
cout << x << endl;
}
void fun()
{
int x = 10; // Local variable
cout << x << endl;
}
x 4
void main()
{
x = 4;
fun();
cout << x << endl;
}
2
void fun()
{
int x = 10;
cout << x << endl;
}
x 10
3
51. 51
Example of Defining and Using
Global and Local Variables
#include <iostream.h>
int x; // Global variable
Void fun(); // function signature
void main()
{
x = 4;
fun();
cout << x << endl;
}
void fun()
{
int x = 10; // Local variable
cout << x << endl;
}
x 4
void main()
{
x = 4;
fun();
cout << x << endl;
}
2
void fun()
{
int x = 10;
cout << x << endl;
}
x 10
4
52. 52
Example of Defining and Using
Global and Local Variables
#include <iostream.h>
int x; // Global variable
Void fun(); // function signature
void main()
{
x = 4;
fun();
cout << x << endl;
}
void fun()
{
int x = 10; // Local variable
cout << x << endl;
}
x 4
void main()
{
x = 4;
fun();
cout << x << endl;
}
2
void fun()
{
int x = 10;
cout << x << endl;
}
x 10
5
53. 53
Example of Defining and Using
Global and Local Variables
#include <iostream.h>
int x; // Global variable
Void fun(); // function signature
void main()
{
x = 4;
fun();
cout << x << endl;
}
void fun()
{
int x = 10; // Local variable
cout << x << endl;
}
x 4
void main()
{
x = 4;
fun();
cout << x << endl;
}
6
54. 54
Example of Defining and Using
Global and Local Variables
#include <iostream.h>
int x; // Global variable
Void fun(); // function signature
void main()
{
x = 4;
fun();
cout << x << endl;
}
void fun()
{
int x = 10; // Local variable
cout << x << endl;
}
x 4
void main()
{
x = 4;
fun();
cout << x << endl;
}
7
55. 55
II. Using Parameters
Function Parameters come in three
flavors:
Value parameters – which copy the values of
the function arguments
Reference parameters – which refer to the
function arguments by other local names and
have the ability to change the values of the
referenced arguments
Constant reference parameters – similar to
the reference parameters but cannot change
the values of the referenced arguments
56. 56
Value Parameters
This is what we use to declare in the function signature or
function header, e.g.
int max (int x, int y);
Here, parameters x and y are value parameters
When you call the max function as max(4, 7), the values 4 and 7
are copied to x and y respectively
When you call the max function as max (a, b), where a=40 and
b=10, the values 40 and 10 are copied to x and y respectively
When you call the max function as max( a+b, b/2), the values 50
and 5 are copies to x and y respectively
Once the value parameters accepted copies of the
corresponding arguments data, they act as local
variables!
57. 57
Example of Using Value
Parameters and Global Variables
#include <iostream.h>
int x; // Global variable
void fun(int x)
{
cout << x << endl;
x=x+5;
}
void main()
{
x = 4;
fun(x/2+1);
cout << x << endl;
}
x 0
void main()
{
x = 4;
fun(x/2+1);
cout << x << endl;
}
1
58. 58
Example of Using Value
Parameters and Global Variables
#include <iostream.h>
int x; // Global variable
void fun(int x)
{
cout << x << endl;
x=x+5;
}
void main()
{
x = 4;
fun(x/2+1);
cout << x << endl;
}
x 4
void main()
{
x = 4;
fun(x/2+1);
cout << x << endl;
}
2
void fun(int x )
{
cout << x << endl;
x=x+5;
}
3
3
59. 59
Example of Using Value
Parameters and Global Variables
#include <iostream.h>
int x; // Global variable
void fun(int x)
{
cout << x << endl;
x=x+5;
}
void main()
{
x = 4;
fun(x/2+1);
cout << x << endl;
}
x 4
void main()
{
x = 4;
fun(x/2+1);
cout << x << endl;
}
2
void fun(int x )
{
cout << x << endl;
x=x+5;
}
3
4
8
60. 60
Example of Using Value
Parameters and Global Variables
#include <iostream.h>
int x; // Global variable
void fun(int x)
{
cout << x << endl;
x=x+5;
}
void main()
{
x = 4;
fun(x/2+1);
cout << x << endl;
}
x 4
void main()
{
x = 4;
fun(x/2+1);
cout << x << endl;
}
2
void fun(int x )
{
cout << x << endl;
x=x+5;
}
3
8
5
61. 61
Example of Using Value
Parameters and Global Variables
#include <iostream.h>
int x; // Global variable
void fun(int x)
{
cout << x << endl;
x=x+5;
}
void main()
{
x = 4;
fun(x/2+1);
cout << x << endl;
}
x 4
void main()
{
x = 4;
fun(x/2+1);
cout << x << endl;
}
6
62. 62
Example of Using Value
Parameters and Global Variables
#include <iostream.h>
int x; // Global variable
void fun(int x)
{
cout << x << endl;
x=x+5;
}
void main()
{
x = 4;
fun(x/2+1);
cout << x << endl;
}
x 4
void main()
{
x = 4;
fun(x/2+1);
cout << x << endl;
}
7
63. 63
Reference Parameters
As we saw in the last example, any changes in
the value parameters don’t affect the original
function arguments
Sometimes, we want to change the values of the
original function arguments or return with more
than one value from the function, in this case we
use reference parameters
A reference parameter is just another name to the
original argument variable
We define a reference parameter by adding the & in
front of the parameter name, e.g.
double update (double & x);
64. 64
Example of Reference Parameters
#include <iostream.h>
void fun(int &y)
{
cout << y << endl;
y=y+5;
}
void main()
{
int x = 4; // Local variable
fun(x);
cout << x << endl;
}
void main()
{
int x = 4;
fun(x);
cout << x << endl;
}
1 x
? x
4
65. 65
Example of Reference Parameters
#include <iostream.h>
void fun(int &y)
{
cout << y << endl;
y=y+5;
}
void main()
{
int x = 4; // Local variable
fun(x);
cout << x << endl;
}
void main()
{
int x = 4;
fun(x);
cout << x << endl;
}
2
x
? x
4
void fun( int & y )
{
cout<<y<<endl;
y=y+5;
}
3
66. 66
Example of Reference Parameters
#include <iostream.h>
void fun(int &y)
{
cout << y << endl;
y=y+5;
}
void main()
{
int x = 4; // Local variable
fun(x);
cout << x << endl;
}
void main()
{
int x = 4;
fun(x);
cout << x << endl;
}
2
x
? x
4
void fun( int & y )
{
cout<<y<<endl;
y=y+5;
}
4 9
67. 67
Example of Reference Parameters
#include <iostream.h>
void fun(int &y)
{
cout << y << endl;
y=y+5;
}
void main()
{
int x = 4; // Local variable
fun(x);
cout << x << endl;
}
void main()
{
int x = 4;
fun(x);
cout << x << endl;
}
2
x
? x
9
void fun( int & y )
{
cout<<y<<endl;
y=y+5;
}
5
68. 68
Example of Reference Parameters
#include <iostream.h>
void fun(int &y)
{
cout << y << endl;
y=y+5;
}
void main()
{
int x = 4; // Local variable
fun(x);
cout << x << endl;
}
void main()
{
int x = 4;
fun(x);
cout << x << endl;
}
6
x
? x
9
69. 69
Example of Reference Parameters
#include <iostream.h>
void fun(int &y)
{
cout << y << endl;
y=y+5;
}
void main()
{
int x = 4; // Local variable
fun(x);
cout << x << endl;
}
void main()
{
int x = 4;
fun(x);
cout << x << endl;
}
x
? x
9
7
70. 70
Constant Reference Parameters
Constant reference parameters are used under
the following two conditions:
The passed data are so big and you want to save
time and computer memory
The passed data will not be changed or updated in
the function body
For example
void report (const string & prompt);
The only valid arguments accepted by reference
parameters and constant reference parameters
are variable names
It is a syntax error to pass constant values or
expressions to the (const) reference parameters