1. Programming Fundamental
Instructor Name: Muhammad Safyan
Lecture-12

2. Lecture outline Function: Call By Value Function Call By Reference
Scope of Identifiers

3. Functions

4. Function Steps involve in functions: Declare a function
Define a function
Call a function

5. Calling function
Called function

6. Area of the Ring Inner Circle Outer Circle Area of Outer Circle
____
Area of Inner Circle
Area of Outer Circle
= Area of the Ring

7. Calculating ringArea without using Function
main ( ) {
ringArea = ( * rad1 * rad1 ) – ( * rad2 * rad2 ) ; }

8. Example: Function to calculate the area of a ring
(with Return Value)

9. Example: Function to calculate the area of a ring
(Without Return a value)

10. Call By Value

11. Formal and Actual Parameters
formal parameter — the identifier used in a method to stand for the value that is passed into the method by a caller.
For example, amount is a formal parameter of process Deposit.
actual parameter — the actual value that is passed into the method by a caller.
For example, the 200 used when process Deposit is called is an actual parameter.

12. Call By Value #include <iostream.h > Void f ( int ) ; main ( ) {
int i = 10 ;
cout << “In main i = " << i ;
f ( i ) ;
cout << " Back in main, i = " << i ; }
void f( int i ) {
cout << "In function f , i = " << i ;
i *= 2 ;
cout << "In function f , i is now = “ << i ; }

13. int square( int );
main() {
int a = 10;
cout << a << " squared: " << square( a ) << endl;
Getch(); }
int square( int x )
return x * x;

14. Call Value

15. Call Value

16. Call By Value

17. Use of Function in IF Condition
We can also use a function in the conditional statements like:
if ( isEven ( number ) )

18. #include <iostream>
#include <conio.h>
using namespace std;
int isEven(int);
main ( ) {
int number;
cout << " Please enter the number: " ;
cin>>number ;
if ( isEven ( number ) )
cout << " The number entered is even " << endl; }
else
cout << " The number entered is odd " << endl;
getch();
int isEven ( int number )
if ( 2 * ( number / 2 ) == number )
return 1;
return 0;

19. Call By Reference

20. Reference &x Int j=2; Int &x=j‘;
int &y; // Error: y must be initialized

21. Reference int main() { int x = 3; int &y = x;
cout << "x = " << x << endl << "y = " << y << endl;
y = 7;
Getch(); }

22. CallByReference
In ‘Call By Reference’, we are not passing the value itself but
some form of reference or address.
To understand this,
you can think in terms of variables which are names of memory locations. We always access a variable by its name (which in fact is accessing a memory location), a variable name acts as an address of the memory location of the variable.

23. CallByReference
we can’t pass the value. We have to pass the memory address of the value. This introduces a new mechanism which is achieved by using ‘&’ (ampersand) operator in C language. This ‘&’ operator is used to get the address of a variable.

24. Call by Reference Example
void squareByReference( int & );
int main() {
int z = 4;
cout << "z = " << z << " before squareByReference" << endl;
squareByReference( z );
cout << "z = " << z << " after squareByReference" << endl;
getch(); }
void squareByReference( int &numberRef )
numberRef *= numberRef;

25. Example

28. Scope of Identifiers
Identifier is any name user creates in his/her program
Functions are also identifiers
Labels are also identifiers

29. Scope of Identifiers Scope means visibility
A variable declared inside a block has visibility within that block only
Variables defined within the function has a scope that is function wide

30. Example
void functionName ( ) {
int i ; }
…..

31. Identifiers Important Points
Do not create variables with same name inside blocks, inside functions or inside bigger blocks
Try to use separate variable names to avoid confusion
Reuse of variables is valid

32. File Scope
# include < iostream.h >
int i ;
Global variable

33. Global Variable Can be used anywhere in program
Can cause logical problems if same variable name is used in local variable declarations
For good programming
Try to minimize the use of global variables
Try to use local variables as far as possible

34. Visibility of Identifiers
Global Scope
Anything identified or declared outside of any function is visible to all functions in that file
Function level scope
Declaring variables inside a function can be used in the whole function
Block level scope
Variables or integers declared inside block are used inside block

35. for ( int i = 0 ; i < 10 ; i++ )
Example: Block Scope
for ( int i = 0 ; i < 10 ; i++ )
It is block level scope declared in for loop
When for is finished “ i ” no longer exists

36. Example: Global Scope using namespace std; int i ; void f () ; main(){
i=10;
cout<<"within main i ="<<i<<endl ;
f() ;
cout<<"after calling f() i ="<<i<<endl ;
getch(); }
void f ()
cout<< "Inside function f , i =" << i<<endl ;
i=20 ;