Chp8_C++_Functions_Part2_User-defined functions.pptx

User-defined functions
Ali Alsbou
functions : Part II

Introduction :
• A complex program is often easier to solve by dividing it
into several smaller parts, each of which can be solved by
itself This is called structured programming.
• These parts are sometimes made into functions in C++.
• All C++ programs must contain the function main( ).
• The execution of the program starts from the function
main( )
2
C++
Programming,
Ali
Alsbou

Advantages of Functions
• Functions make programs easier to write, debug,
and understand.
• Functions can be called several times in the same
program, allowing the code to be reused.
3
C++
Programming,
Ali
Alsbou

Need to know
• Functions invoked by a function–call-
statement which consist of it’s name and
information it needs (arguments)
functionName (argument);
• All other functions are directly or
indirectly called from main.
• The purpose of a function is to receive
data, process it and return a value to the
function which has called it.
4
C++
Programming,
Ali
Alsbou

User-defined functions
• Standard C++ Library is still not sufficient for
most programming tasks.
• Programmers also need to be able to define
their own functions
5
C++ Programming, Ali Alsbou

function–call Principle
• Boss To Worker
A Boss (the calling/caller function) asks a worker (the
called function) to perform a task and return result when it
is done.
6

7
C++ program Flow of Control
The following diagram shows how the flow control
of a program is changed by functions.
Note: usual main( ) Calls other
functions, but other functions
can call each other
C++
Programming,
Ali
Alsbou

Function Definitions :
How to write :
8
Function definition format
return-value-type function-name( type parameter-list )
{
declarations and statements
return;
}
1) Return-value-type: data type of the result (default int)
void – indicates that the function returns nothing
2) Function-name: any valid identifier
3) Parameter-list: comma separated list, declares parameters
A type must be listed for each parameter
The function header
2 3
4
5
1
Each function has its own
name. Function name
follows rules of naming
identifiers as variables
and constants

Function definition format
return-value-type function-name( type parameter-list )
{
declarations and statements
return;
}
4) function body (block)
 Variables can be defined inside blocks (can be nested)
 Functions can not be defined inside other functions
5) Returning control :Function return ONLY one value
If nothing returned
• return;
• or, until reaches right brace
If something returned
• return expression;
4
5

Function return value types
10
int f1(Parameter List)
{
return value ;
}
void f2(Parameter List)
{
return; // nothing returned
}
void f2(Parameter List)
{
// nothing returned
}
If return type is
missing, it means int.
f2(Parameter List)
{
}
1
3
4
2
void Function
A function that is not
supposed to return a
value(RETURN result)
has a return type of
void.

Function Parameters
• The purpose is to allow passing arguments to the function from the
location where it is called from.
• Parameters declared in the function header within parenthesis
• Either have a single, multiple parameters or have no parameters
• List of a parameters are separated by commas
• Each parameter must be defined as follows
DataType parameterName
• Note : The parameters may or may not be altered by the function.
11
char f1(int x, int y)
{
return value ;}

Exercises(1)
• Write C++ functions that :
• Find summation of two integer number(as parameters) and
return result.
• Find subtraction of two integer number(as parameters) and
return result.
• simply prints any message.

Examples (1)
13

Example (2)
14
Write a function to compute n!

General form of C++ program with functions
15
The function definition can be placed anywhere in the
program after the function prototypes.

Function Prototypes(declaration)
• Prototype only needed if function definition comes after use in program
• Alternative to Prototype is to place function definition before main() function
• Write the Function prototype after include<> statements, and before main
function.
• Function prototype statement is a function definition header
terminated by the semicolon;
• The general form of the declaration is
Return_ type function_ name ( parameter_ list );
 Prototype must match function definition header
int square(int y);
16
int square(int);
Note : The variables in the
function declaration can be
optional but data types are
necessary

Function prototype : Con’t
• Function Definition
double maximum(double x,double y,double z)
{
… }
• Function prototype
double maximum(double x,double y,double z);
Or
double maximum(double , double , double );
17

Example (3) : Function Prototypes
1. double CircleArea(double radius);
2. double CircleArea(double);
3. int calculation(int n,float j);
4. int calculation (int,float);
5. int calculation (int n,float);
6. double computeTax(double income);
18

Using Function
How Function Call Works
19
Functions invoked by a function–call-statement which consist of it’s name and
information it needs (arguments)
functionName (argument);
 Each value passed in a function call is referred to as an Argument
- Arguments may be constant value ,variable or expression
 Arguments passed by value and by reference (later .)
 Arguments (Passed in a Function call) and parameters (defined in a function
header) MUST match in: Number , Order and Data types
void Display_Msg(int x)
{
if (x > 60)
cout<<"You passed";
else
cout<<“You failed";
}
int main()
{
Display_Msg(87);
return 0;
}
Argument
Parameter

Using Function
How Function Call Works – Cont.
20
if function return value:
int func1(int value)
{
result=value;
return result;
}
Use func. Calling statement with :
- Variable Ex. x= func1(3);
- output statement Ex. cout<< func1(3)
- Expression Ex. x=func1(3)+5- func1(4);

Function–call-statement
Example
21
function–call-statement:
• cout<<square (2);
• cout<<square (2+6);
• y=2;
X= square (y); // X= 4
• if (square (y) > 2) cout <<“True”;
• for( int c=0; c> square (2);c--) …..

Function–call-statement
Example
• if function return nothing (void function):
void func1(int value)
{
result=value;
return; // or no need to write this
}
• Use func. Calling statement like:
func1(3); //since this function return nothing

Function Call Methods
Passing mechanism
Two ways to pass arguments to functions
• Call by value
• Call by reference (memory locations )
 Mixed Methods
Parameter lists can include pass-by-value and pass-by-reference parameters
23

Call by value
 A copy of the value is passed
 a copy of the parameters value is taken from the calling function
and passed to the called function
 Suppose that :
void exam(int b); func. Prototype
a=27;
exam(a); func. calling
24
All the pervious examples used this method
27 27
a
b
B=b++;
27 28
a b
copy of a

Example (4)
 a copy of the parameters value is
taken from the calling function and
passed to the called function

Example(6)
1.// Creating and using a programmer-defined function.
2.#include <iostream.h>
3. int square( int ); // function prototype
4. int main( ) {
1.for ( int x = 1; x <= 10; x++ )
2.cout << square( x ) << " "; // function call statement
3.cout << endl;
4.return 0; // indicates successful termination
5. } // end main
6.int square( int y ) // y is a copy of argument to function
7. {
8. return y * y; // returns square of y as an int
9. } // end function square
27
1 4 9 16 25 36 49 64 81 100

Example(7)
Write a program to find the average of three integer marks (use functions)?
28
#include<iostream.h>
float avg(int,int,int); //function prototype
main() {
int m1,m2,m3;
cout <<"Enter three marks :";
cin>>m1>>m2>>m3;
cout <<"The average is : "<<
avg(m1,m2,m3); //function calling
}
float avg(int a,int b , int c) //function definition
{
float d;
d=(a+b+c)/3.0;
return d;
}

Example(8)
int max (int a,int b,int c);
main() {
int x,y,z,m;
cout <<"Enter three numbers :";
cin>>x>>y>>z;
m = max(x,y,z);
cout <<"the maximum number is "<< m;
}
int max (int a,int b,int c) {
int m=a;
if (m<b) m=b;
if (m<c) m=c;
return m; }
29
int max (int a,int b,int c)
{
int m=a;
if (m<b) m=b;
if (m<c) m=c;
return m;
}
main()
{
int x,y,z,m;
cout <<"Enter three numbers :";
cin>>x>>y>>z;
m = max(x,y,z);
cout <<"the maximum number is "<< m;
}
1 2

Example (9)
Write C++ program, using function, to find the summation of
the following series:
30
int summation ( int x)
{
int i = 1, sum = 0;
while ( i <= x )
{
sum += i * i ;
i++;
}
return (sum);
}
main ( )
{
int n ,s;
cout << "enter positive number"
cin >> n;
s = summation ( n );
cout << "sum is: " << s << endl;
}

Example(10)
void Function take no arguments
If the function Does Not Take
Arguments specify this with
EMPTY-LIST OR write void
inside
void funA();
void funB(void)
main()
{
funA();
funB();
return 0; }
void funA()
{ cout << "Function-A takes no arqumentsn"; }
void funB()
{ cout << "Also Function-B takes No argumentsn"; }
Will be the same
in all cases

Example(11)
#include <iostream.h>
void even (int);
main() {
for( int i=20;i<35;i++)
even(i);
}
void even (int x) {
if(x %2==0)
cout<<x<<" "; }
32
Print the even numbers between (20,35) using function void even (int);

Call by reference
• This method is more efficient and provides
higher execution speed than the call by value
method, but call by value is more direct and
easy to use.
• gives the called function the ability to directly
access the caller’s value, and to modify it.
33

Call by reference
• The argument to a reference parameter must be a
variable, not a constant or an expression
• "address of " actual argument is passed
• The parameter in function definition must be
prefixed with ampersand(&)
void fname (type &);// prototype
main()
{
fname(argument);
}
void fname(type &parameter_name)
{
… }
// passing address of argument

Example(12)
void increment (int );
int main ()
{
int a=5;
increment(a);
cout<<a<<endl;
return 0;
}
void increment (int z) 35
void increment (int &);
int main ( )
{
int a=5;
increment(a);
cout<<a<<endl;
return 0;
}
void increment (int &z)
{ z++; }
Call by reference
Call by value
//Value a is copied to z;

Example(13)
#include<iostream>
int square(int); //prototype call by value function
void squarref(int &); // prototype call by –reference function
int main()
{
int x=2, z=4;
cout<< "x=" <<x << " before calling squareVal"<<endl;
square(x) ; // call by value
cout<< "x=" <<x << " After returning"<<endl;
cout<< "z=" <<z << " before calling squareRef"<<endl;
squarref(z); // call by reference
cout<< "z=" <<z<< " After returning squareRef"<<endl;
return 0;
}
36
void square(int a)
{
a*=a;
// caller’s argument not modified
}
void squarref(int &cRef)
{
cRef *= cRef;
// caller’s argument modified
}

Example(14):
swap Function
// swap() function definition
void swap(double & num1, double &
num2)
// swap the values of num1 and num2
{
double temp;
temp = num1; // Why do we need temp?
num1 = num2;
num2 = temp;
}
37
swap(oneNum, anotherNum);

Example(15)
float rectangle(float width, int &height)
{
float area; // Area of the rectangle
area = width * height ;
return (area);
}
int main()
{ int h=3;
float area=rectangle(2,h);
cout<< area;
return 0; } 38

Illegal function Call
Void calc(double l,double w,double & a,double & p);
Suppose that :
double a =3.0,b=4.0,c=5.0,d= 6.0,e=7.0;
const double x = 5.0, y = 6.0;
The following function calls are illegal:
• calc(3.0, 4.0, 5.0, 6.0);
• calc(a, b, 5.0, 6.0);
• calc(a, b, c*d, e);
• calc(a, b, x, y);
39

Exercise(2)
Suppose that :
double circleArea(double & radius);// Pass by reference
double r=2.5;
Where is the errors in the following statements?
area1 = circleArea(3*r+2.0);// SYNTAX ERROR!
area2 = circleArea(3.5); // SYNTAX ERROR!
40

Global vs. local variables
41

Global vs. local variables
Scope of variable :
• A scope (the part of the program code that can use it)
Global variables :
• defined outside and before function main:
• all functions can see it and using it and can be
accessible and used anywhere in the entire program.
(Scope)
• Global variables can live as long as the program is
executed
42

Example(16)
Global variables :
int x = 0; // global variable
void f1( )
{ x++; }
void f2( )
{
x+=4;
f1( );
}
main( ) {
f2( );
cout << x << endl; }
43

Local variables :
• Local variables are declared inside the function body
and exist as long as the function is running and
destroyed(de-allocated) 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
• A local variable can be used only in the function
where it is defined
44

Example(17)
int x=99; // Global variable
Void fun();
void main()
{
int x = 4; // loacl variable
fun();
cout << x << endl;
}
void fun()
{
int x = 10; // Local variable
cout << x << endl;}
45

Example(18)
int x,y; //Global Variables
int add2(int, int);
main()
{ int s;
x = 11;
y = 22;
cout << "global x=" << x << endl;
cout << "Global y=" << y << endl;
s = add2(x, y);
cout <<x <<"+" << y << "=" << s;
cout<<endl;
cout<<"n---end of output---n";
return 0; }
46
int add2(int x1,int y1)
{
int x; //local variables
x=44;
cout << "nLocal x=" << x << endl;
return x1+y1;
}

Example(19)
void f(void);
main ( )
{
f();
f();
f();
}
void f(void)
{
int x=0;
x++;
cout<<x<<endl;
}
47

Static vs. Automatic variables
• Normal” local variables go out of scope and are de-
allocated when a function terminates.
• Static variables remain and retain their value.
• Format:
• When declare static variable it initializes to 0 unless
you specify another value
48
void f( )
{
static <variable_type> <variable_name>
…
}

Example(21)
void my_function ( )
{
int count = 1;
cout<<"this function has been called "<<count<<"n";
count++;
return;
}
int main(){
my_function();
my_function();
my_function();
return 0; }
49

Example(21)- Cont.
void my_function ( )
{
static int count = 1;
cout<<"this function has been called "<<count<<"n";
count++;
return;
}
int main(){
my_function();
my_function();
my_function();
return 0;}
50

Example(22)
#include <iostream>
void showstat( int curr )
{
static int nStatic;
nStatic += curr;
cout << "nStatic is " << nStatic << endl;
}
int main()
{
for ( int i = 0; i < 4; i++ )
showstat( i );
}
51
nStatic is 0
nStatic is 1
nStatic is 3
nStatic is 6

Arrays &Functions
52

Passing Arrays to Functions
• To pass an array argument to a function
Specify array name without brackets
Array a is declared as
int a[ 24 ];
The function call
modifyArray( a, 24 );
passes array a and its size to function modifyArray
• Array size is normally passed as another argument
so the function can process the specific number of
elements in the array
• Arrays are passed by reference (Function call actually passes starting
address of array )
53

Passing Arrays to Functions (Cont.)
• Individual array elements passed by value
Use the subscripted name of the array element as an argument
Example:
modifyElement( a[ 3 ] );
void modifyElement( int e )
{
cout << "Value of element in modifyElement: " << ( e *= 2 ) << endl;
}
54
Function Calling
Function definision

Functions that take arrays as arguments
• Function definition
Example:
void modArray( int b[], int arraySize );
• Array parameter may include the size of the array
• Compiler will ignore it, though Compiler only cares about
the address of the first element
55

Exercise(3)
Using function, write a program to read array items then print them
56
void read (int [],int);
void print(int [],int);
main()
{
int R[5];
read (R,5);
print(R,5);
} void print (int F[],int x)
{
int i;
for(i=0;i<x;i++)
cout<<F[i]<<" ";
}
void read (int M[],int n)
{
int i;
for(i=0;i<n;i++)
{
cout <<"Enter item number "<<i<<" : ";
cin>> M[i];
} }

Passing 2D-array to function
you must determine the size of column in two
dimension array
57

Example(23)
void printArray (int [][3]) ;
int main ( )
{
int array1[2][3]={{1,2,3},{4,5,6}};
cout<<"Array1=";
printarray(array1);
}
void printarray (int a[][3])
{
for (int i=0 ; i<2 ; i++)
{
for (int j=0 ; j<3 ; j++)
cout<<a[i][j];
cout<<endl;
} } 58

Recursive Function ( Recursion) :
A function that calls itself
A recursive function has two parts:
1) the terminal/base case.
a stopping condition
2) the reducing case/recursive step
an expression of the computation or definition in terms of itself
Every recursive call reduces the original problem,
bringing it increasingly closer to a base case until it
becomes that case.
59

General algorithm for recursion
60
if (terminal_condition)
terminal_case
else
reducing_case
if (!terminal_condition)
reducing_case

Example(24):
print numbers counting down
# include<iostream>
void print(int n)
{
if (n==0)
return;
cout<<n<<endl;
print(n-1);
}
61
int print2(int n)
{
if (n==0)
return 1;
cout<<n<<endl;
return print2(n-1);
}
main( )
{
int n;
cin>>n;
print(n);
cout<<print2(n);
}

Factorials by recursion
• Easy way to calculate n!
• n! = 1 if n == 1 or n==0
• Otherwise, n! = n * (n-1)!
62

Example(25):
Factorials by recursion – Cont.
int factorial (int n);
main ( )
{ int n;
cin>>n;
cout<<factorial(n); }
int factorial (int n)
{
if (n==1 || n==0) // base case
return 1;
else
return n * factorial(n-1); // recursive part
}
63
recursive step
terminal_case

Recursive function
Find X to the power n
• Terminal case
if n==0 since x to powr 0 is =1
• Recursive case
x * power(x,n-1)
64

Example(26)
65
int power (int x , int n );
main ( ) {
int x,y;
cout<<"enter two numbern";
cin>>x>>y;
cout<<power(x,y);}
int power (int x, int n )
{
if (n==0)
return 1; // base case
else
return x* power(x,n-1); // recursive part
}

Example(27):
66
Write a recursive function to find the sum of the first 4 elements of an
integer array "a[ ]".

Note about recursion function
• Infinite recursion
Any recursive function that not bringing it to a base
case
68

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