FunctionFunction

User defined function is a code segment (block) that perform an specific action.

Function Definition:Function Definition:Return_DT F_name ( list of formal parameters) { Action_ body ; }

The Function Definition

Function are of 4 types:1- A function that doesn’t return a value without

argument -Return_DT is void

-Action_body doesn’t contain return statement.

Syntax: void function-name ( )

{ local declarations // this is optional executable statements }

Example: function that doesn’t return a value without arguments

void print_O ( ){ cout << “ ** “ << endl; cout << “ * * “ << endl; cout << “ * * “ << endl; cout << “ ** “ << endl;}

The Function Definition

2- A function that doesn’t return a value with arguments

-Return_DT is void -Action_body doesn’t contain return statement.

Syntax: void function-name(argument_list) { local declarations // this is optional executable statements }

Example: function that doesn’t return a value with arguments

void print_box (int n) { cout << “* * * * * * *\n” ;

cout << “* “ << n << “ * \n” ; cout << “* * * * * * *\n” ; }

The Function Definition

3- A function that returns a result of any type without arguments

-Return_DT is any type -Action_body contains return statement.

Syntax: <any type> function-name( ) { local declarations // this is optional executable statements }

Example: function that return a value without arguments

int sum (){ int x=5, y=7 ;return x+y ;}

The Function Definition

4- A function that returns a result of any type with arguments

-Return_DT is any type -Action_body contains return statement.

Syntax: <any type> function-name(argument_list ) { local declarations // this is optional executable statements }

Example: function that return a value with arguments

int Rect_area (int L, int W){ int a ; a = L * W ; return a ;}

Calling (invoking) Function:Calling (invoking) Function:

a) The call to a Function that does not return a value is given in the following syntax:

F_name (Actual parameters); e.g. draw_circle ( ); e.g. sum(4,7);b) The call to a Function that returns a value is given as follows: - The name of the functio is given within the output statement e.g cout<<sum(x,y); - The name of the Function is given within the assignment statement e.g. result = sum (x, y );

The Call to a function

program Figure Function draw_circle

void main(){ ------- -------draw_circle ( ); ------ ------ ------}

void draw_circle ( ) { ------ ------ ------ ------}

call

return

ExampleExample

#include <iostream.h>int Max (int Value1, int Value2) {

if (Value1 > Value2)return Value1;

elsereturn Value2;

}

void main() {int a, b;cout<<"\nPlease Enter the values of a and b: ";cin>>a>>b;cout<<"\n the maximum one is: "<<Max(a,b)<<endl;

}

Function Definition

Calling the function in an expression like cout<<, condition, assignment

statements

ExampleExample

#include <iostream.h>int Max (int Value1, int Value2) {

if (Value1 > Value2)return Value1;

elsereturn Value2;

}

void main() {int a, b;cout<<"\nPlease Enter the values of a and b: ";cin>>a>>b;cout<<"\n the maximum one is: "<<Max(a,b)<<endl;

}

ExampleExample

#include <iostream.h>int Sum (int A, int B) {

return (A+B); }

void main() {int N1, N2, S;cout<<"\n Please Enter N1 and N2: ";cin>>N1>>N2;S = Sum(N1,N2);cout<<"\nSum= "<<S<<endl;

}

ExampleExample#include <iostream.h>bool Positive (int Num) {

if (Num > 0)return true;

elsereturn false;

}void main() {

int Number;cout<<"\nEnter Number: ";cin>> Number;if (Positive(Number))

cout<<"\n the number is positive";else

cout<<"\n the number is negative";cout<<endl;

}

ExampleExample

#include <iostream.h>float Area (int R) {

return (3.14 * R * R );}

void main() {int Radius;cout<<"Enter the Redius: ";cin>>Radius;cout<<"\nCircle Area is: "<<Area(Radius);cout<<endl;

}

ExampleExample#include <iostream.h>long Power(int Base, int Exp) {

int M=1;for(int i=1; i<=Exp; i++)

M*=Base;return M;

}

void main() {int B, E;cout<<"\nEnter Base: ";cin>>B;cout<<"\nEnter Exponent: ";cin>>E;cout<<"\n Result= "<<Power(B,E);cout<<endl;

}

ExampleExample#include <iostream.h>long Fact (int Num) {

int F = 1, i = Num;while (i>=1){

F *= i;i--; }

return F;}

void main() {int Number;cout<<"Enter an integer number: ";cin>>Number;cout<<endl<<Number<<"!= "<<Fact(Number);cout<<endl;

}

Void Returned Data TypeVoid Returned Data Type#include <iostream.h>void Print(char Ch, int n) {

for (int i=1; i<=n; i++)cout<<Ch;

cout<<endl;}

void main() {char Sym;int Number;cout<<"\nEnter the Symbol: ";cin>>Sym;cout<<"\nHow many times: ";cin>>Number;Print(Sym,Number);

}

No Return Statement

ExampleExample

#include <iostream.h>int Mul(int V1, int V2) {

return V1 * V2; }

void Result() {cout<<"\n5 x 9 = "<<Mul(5,9);cout<<"\n4 x 7 = "<<Mul(4,7);cout<<"\n6 x 4 = "<<Mul(6,4)<<endl; }

void main() {Result() ;

}

The Function Prototype• Like other identifiers in C++, function must be declared before it can be

referenced.• To declare a function, we can insert a function prototype before the main

function.

• The function prototype provides all information that the C++ compiler needs to know to translate calls to the function correctly.

• A function prototype tells the compiler the - data type of the function - the function name - information about the arguments that the function expects.• Examples: void draw_circle ( ); int m ( ) ; void print_box (int) ; int Rect_area (int , int);

Function PrototypeFunction Prototype#include <iostream.h>int Mul(int, int);int Add(int, int);void Show();

void main() {Show(); }

int Mul(int X, int Y) { return X*Y; }

int Add(int X, int Y) { return X+Y; }

void Show() {int A=10, B=20;cout<<Add(A,B)<<'\t'<<Mul(A,B)<<endl; }

Function Prototype contains only data types

But may contain identifiers.

Scope of Variables

(1) Global variables: - Those variables that are declared before the main

function. - These are visible from any point of the code, inside

and outside any function.(2) Local variables: - These are declared inside a block or a function. - The scope of local variables is limited to the same nesting level in which they are declared.

Example of Local and Global Variables

// File: global.cpp#include <iostream.h>int x = 7 ; // global variablesint fun1 (int ); // function prototypevoid main ( ){ int z ; // local variable in main cout << “The global variable: “ << x ; z = fun1 ( 5 ) ; // calling add function cout << “ The result is “ << z << endl ;}int fun1 ( int a ){ int r ; // local variable in fun1 r = a * a * a ; return r ; }

Functions and Passing Parameters

The mechanisms of passing parameters: (1) Call by value: - During the function call, the value of the argument is found and passed to the function. - Any modification inside the function does not affect the argument.

(2) Call by reference: - During the function call, the address of the variable is passed to the function. - Any modification made on the parameter inside the function will have effect in the passed variable outside it.

Difference between Function Definitions for Call by Value and Call by Reference

• For call by value, we declare the arguments of the function as usual.

Example: int func1 ( int , int ); // function prototype

• For call by reference, the type of the argument is followed by the symbol (&) to specify that the variable has to be passed by reference.

Example: void func2 ( int & , int & ); // function prototype

Call by valueCall by valueWhen calling, the value of actual parameter will be copied to the formal parameter.

#include <iostream.h>void Increment(int);

void main() {int A = 10;Increment(A);cout<<A<<endl;

}

void Increment(int X) { ++X; }

Call By referenceCall By referenceWhen calling, the reference formal parameter will be an alternative name to the actual parameter.

#include <iostream.h>void Increment(int&);

void main() {int A = 10;Increment(A);cout<<A<<endl;

}

void Increment(int &X) { ++X; }

Call By referenceCall By referenceWhen calling, the pointer formal parameter will points to the actual parameter.

#include <iostream.h>void Increment(int*);

void main() {int A = 10;Increment(&A);cout<<A<<endl;

}

void Increment(int *X) { ++*X; }

Example 5: Call by Value// File: calls1.cpp#include <iostream.h>// function prototype: the arguments to be passed by valueint add (int , int );void main ( ){ int x, y , z ; // local variables in main cout << “ Enter two integers: “ ; cin >> x >> y ; cout << “ x = “ << x << “ y = “ << y << endl; z = add ( x , y ) ; // calling add function cout << “ The result is “ << z ; cout <<“After call “<< “ x = “ << x << “ y = “ << y << endl;}int add ( int a , int b ){ return a + b ; }

Execution of Example 5• The user will be prompted to enter two integers.• The user enters, for example, 10 and 20 that are saved in x and

y respectively.• When function add is called, the value of x and y are passed

to the function.• The function add takes the values 10 and 20 and links them to

a and b respectively.• The function will return the result which is 30.The output: Enter two integers: 10 20 x = 10 y = 20 The result is 30 After call x = 10 y = 20

Example 6: Call by Reference// File: calls2.cpp#include <iostream.h>// function prototype: the arguments to be passed by referencevoid duplicate (int & , int & , int & );void main ( ){ int x, y , z ; // local variables in main cout << “ Enter three integers: “ ; cin >> x >> y >> z ; cout << “ Before call: “ << “ x = “ << x << “ y = “ << y << “ z = “ << z <<endl; duplicate ( x , y , z ) ; // calling duplicate function cout <<“ After call: << “ x = “ << x << “ y = “ << y << “ z = “ << z <<endl;}void duplicate ( int & a , int & b , int & c ){ a *= 2 ; b *= 2 ; c *= 2 ; }

Execution of Example 6• The user will be prompted to enter three integers.• The user enters, for example, 10, 20, and 30 that are saved in x, y,

and z respectively.• When function duplicate is called, the addresses of x, y, and z are

passed to the function.• The addresses of x, y, and z are linked to the parameters of the

function a, b, and c. The function will duplicate each parameter and save the result in the same parameter. Thus,

a becomes 20 hence x becomes 20 also b becomes 40 hence x becomes 40 also c becomes 60 hence x becomes 60 also• After the call we see that the values of x, y, and z are changed.The output: Enter three integers: 10 20 30 Before call: x = 10 y = 20 z = 30 After call: x = 20 y = 40 z = 60

RecursionRecursionFunction call itself

#include <iostream.h>int Fact (int N) {

if (N<=1)return 1;

elsereturn N * Fact(N-1);

}void main() {

cout<<Fact(5)<<endl;}

ExampleExample

#include <iostream.h>int Zap (int N) {

int Z;if (N<=1)

Z=1;else

Z= Zap(N-1) + Zap(N-3);return Z;

}void main() {

cout<<Zap(5)<<endl;}

Array as parameterArray as parameter-Array name is pointer (call by reference)

#include <iostream.h>void Increment (int a[]) {

for (int i=0; i<5; i++)a[i] += 10; }

void main() {int b[5] = {10,20,30,40,50};Increment(b);for(int i=0; i<5; i++)

cout<<b[i]<<'\t';cout<<endl;

}

Array as parameterArray as parameter-Array element (call by value)

#include <iostream.h>void Increment (int a) { ++a; }

void main() {int b[5] = {10,20,30,40,50};Increment(b[1]);cout<<b[1]<<endl;

}