1. Programming fundamentals 2 Chapter 2:Pointer
Miss:Hanan Hardam

2. Pointers in C++ Topics to cover: Overview of Pointers
Pointer Declaration
Pointer Assignment
Pointer Arithmetic

3. Overview of Pointers
A Pointer in C++ is variable whose value is a memory address.
With pointers many memory locations can be referenced.
Some data structures use pointers (e.g. linked list, tree).
The * and & operators
- & operator is the address operator
- * operator is the dereferencing operator. It is used in
pointers declaration

4. Pointer Declaration Pointers are declared as follows:
<type> * variable_name ;
e.g.
int * xPtr; // xPtr is a pointer to data of type integer
char * cPtr; //cPtr is a pointer to data of type character
void * yPtr; // yPtr is a generic pointer,
// represents any type

5. Pointer Assignment
Assignment can be applied on pointers of the same type
If not the same type, a cast operator must be used
Exception: pointer to void does not need casting to convert a pointer to void type
void pointers cannot be dereferenced
Example
int *xPtr, *yPtr; int x = 5; …
xPtr = & x; // xPtr now points to address of x
yPtr = xPtr; // now yPtr and xPtr point to x

6. Cont. Example
int *xPtr, *yPtr; int x = 5;
xPtr = & x;
yPtr = xPtr;

7. Cont. Example
4. cout << *xPtr; // this statement should print the value that is pointed to by xPtr, which is cout<< xPtr; // this statement should print the contents of xPtr location, which is the address The same applies for yPtr, since it points to the same location as xPtr.

8. Pointer Arithmetic Increment / decrement pointers ( ++ or -- )
Add / subtract an integer to/from a pointer
( + or += , - or -= )
Pointers may be subtracted from each other
Pointer arithmetic is meaningless unless performed on an array
This will be discussed in more details in Arrays chapter.

9. Examples on Pointers //File: pointers.cpp
//A program to test pointers and references
#include <iostream.h>
void main ( )
{ int intVar = 10;
int *intPtr; // intPtr is a pointer
intPtr = & intVar;
cout << "\nLocation of intVar: " << & intVar;
cout << "\nContents of intVar: " << intVar;
cout << "\nLocation of intPtr: " << & intPtr;
cout << "\nContents of intPtr: " << intPtr;
cout << "\nThe value that intPtr points to: " << * intPtr; }

10. Call by Reference #include <iostream.h> void Increment(int&);
void main() {
int A = 10;
Increment(A);
cout<<A<<endl; }
void Increment(int &X) { ++X; }

11. Call by Reference #include <iostream.h> void Increment(int&);
//if you add extra cout statements to the program, the output will become:
#include <iostream.h>
void Increment(int&);
void main() {
int A = 10;
cout << “in main “<< &A << endl;
Increment(A);
cout<<A<<endl; }
void Increment(int &X) { ++X;
cout << “in fun “<< X << endl;
cout << “in fun “<< &X << endl;

12. Call by Pointer #include <iostream.h> void Increment(int*);
void main() {
int A = 10;
Increment(&A);
cout<<A<<endl; }
void Increment(int *X) { ++*X; }

13. Call by Pointer
//if you add extra cout statements to the program, the output will become:
#include <iostream.h>
void Increment(int*);
void main() {
int A = 10;
cout << "in main "<< &A<< endl;
Increment(&A);
cout<<A<<endl; }
void Increment(int *X)
{ ++*X;
cout << "in fun X "<< X << endl;
cout << "in fun *X "<< *X << endl;
cout << "in fun &X"<< &X <<endl;

14. Examples on Pointers (Cont.)
//File: swap.cpp
//A program to call a function to swap two numbers using reference parameters
 #include <iostream.h>
void swap(int *, int *); // This is swap's prototype
void main()
{ int x = 5, y = 7;
swap(&x , &y); // calling swap with reference parameters
cout << "\n x is now "<< x << " and y is now " << y << '\n'; }
// swap function is defined here using dereferencing operator ‘*’
void swap(int *a, int *b)
{ int temp;
temp = *a; // here the values which a and b point to are swapped
*a = *b;
*b = temp;