1. Spring Semester 2013 Lecture 7
Programming In C++
Spring Semester 2013
Lecture 7
Programming In C++, Lecture 7 By Umer Rana
Umer Rana

2. Pointers
A variable that holds an address value of the variable is called a pointer variable or simple pointer.
Pointer does not have any data type, it only tells the compiler what kind of variable the pointer point to.
A pointer can hold the address of any variable of the correct type.
A pointer provides a way of accessing a variable without referring to the variable directly.
The address acts as an intermediary between the variable and the program accessing it.
Pointer is a variable that represents the location of a data item, such as variable or an array element.
Programming In C++, Lecture 7 By Umer Rana

3. Pointers
Suppose v is a variable that represents some particular data item.
The address of v’s memory location can be determined by the expression &v, where & is the unary operator (a unary operation is an operation with only one operand), called the address operator, that evaluates the address of its operand.
e.g. int main(void) {
int v;
printf("%d",&v);
getch(); }
Programming In C++, Lecture 7 By Umer Rana

4. Pointers Declaration
Pointer variables, like all other variables, must be declared before, they may be used in C program.
When a pointer variable is declared, the variable name must be preceded by an asterisk(*).
This identifies the fact that the variable is a pointer.
The data type that appears in the declaration refers to the object of the pointer.
Thus a pointer declaration may be written in general terms as :
Data-type *ptr;
Programming In C++, Lecture 7 By Umer Rana

5. Pointers Notation
Now let us assign the address of v to another variable pointer type *ptrInt.
int *ptrInt;
ptrInt = &v; 
The data item represented by v. can be accessed by the expression *ptrInt.
Where * is a unary operator called the indication operator, that operates only on a pointer variable.
Therefore, *ptrInt and v both represent the same data item.
Programming In C++, Lecture 7 By Umer Rana

6. Pointers Show Address int main(void) { int day; int *ptrInt;
ptrInt=&day;
printf("%d",&day);
printf("\n%d",ptrInt);
getch(); }
Programming In C++, Lecture 7 By Umer Rana

7. Pointers Show Values int main(void) { int day=10; int *ptrInt;
ptrInt=&day;
printf("Show Address of the Variable\n");
printf("\n%d",&day);
printf("\n%d",ptrInt);
printf("\n\nShow value of the Variable\n");
printf("\n%d",day);
printf("\n%d",*ptrInt);
getch(); }
Programming In C++, Lecture 7 By Umer Rana

8. Pointers Initializing
Within a variable declaration, a pointer variable can be initialized by assigning in the address of another variable.
Remember that the variable whose address is assigned to the pointer variable must have been declared earlier in the program, for example.
int i; int *ptrInt=&i;
Programming In C++, Lecture 7 By Umer Rana

9. Pointers Initializing
int main(void) {
int day=10;
int *ptrInt=&day;
printf("Show Address of the Variable\n");
printf("\n%d",&day);
printf("\n%d",ptrInt);
printf("\n\nShow value of the Variable\n");
printf("\n%d",day);
printf("\n%d",*ptrInt);
getch(); }
Programming In C++, Lecture 7 By Umer Rana

10. Why Are Pointers Used? To return more than one value from a function.
To pass array and strings more conveniently from one function to another.
To manipulate arrays more easily by moving pointers to them (or to parts of them), instead of moving the arrays themselves.
To communicate information about memory, as in the function malloc(), which returns the location of free memory by using a memory.
Programming In C++, Lecture 7 By Umer Rana

11. Passing Addresses to a Function
void GiveValues(int *,int *);
int main(void) {
int day,day2;
GiveValues(&day,&day2);
printf("\n Day Value is %d \n Day2 Value is %d",day,day2);
getch(); }
void GiveValues (int *ptr1,int *ptr2)
*ptr1=10;
*ptr2=20;
Programming In C++, Lecture 7 By Umer Rana

12. Pointer to Array Notation
Array Notation is really a thinly disguised form of pointer notation. Infect the compiler translates array notation into pointer notation because microprocessor understand pointers not arrays.
e.g. nums[] = {92,81,70,69,10};
In Memory:
nums[0]=92
nums[1]=81
nums[2]=70
nums[3]=69
nums[4]=10
Programming In C++, Lecture 7 By Umer Rana

13. Pointer to Array Notation
void main (void) {
int nums[]={92,81,70,69,58};
int i;
for (i=0;i<5;i++)
printf(“%d\n”,nums[i]); }
Programming In C++, Lecture 7 By Umer Rana

14. Pointer to Array Notation
int nums[]={92,81,70,69,58};
int i;
printf("\nWith Array Notation \n");
for (i=0;i<5;i++)
{ printf("%d\n",&nums[i]);
printf("%d\n",nums[i]); }
printf("\nWith Pointer Notation\n");
{ printf("%d\n",(nums+i));
printf("%d\n",*(nums+i));
&nums[i] & nums[i] is Array Notation
(nums+i) & *(nums+i) is Pointer Notation
Programming In C++, Lecture 7 By Umer Rana

15. Pointer to Array Notation
int temper[7];
int day;
printf("Please Enter the Temperature of the week\n");
for (day=0;day<7;day++) {
printf("\nTemperature of day %d: ",(day+1));
scanf("%d",temper + day); }
printf("\nTemperature of day %d is %d. ",
(day+1),*(temper+day));
Programming In C++, Lecture 7 By Umer Rana

16. Pointer to Array Function
int main(void) {
int array[]={3,5,7,9,11};
int addNum=10, size=5, i;
addcon(array,size,addNum);
for(i=0;i<size;i++)
printf("\n%d",*(array+i)); }
void addcon(int *ptr,int size,int con)
int i;
for (i=0;i<size;i++)
*(ptr+i)=*(ptr+i)+con;
Programming In C++, Lecture 7 By Umer Rana

17. Pointer to String Notation
Strings are arrays of character so String Notation is thinly disguised form of pointer notation. Infect the compiler translates string notation into pointer notation because microprocessor understand pointers .
Void main (void) {
Char *salute = “Greetings”;
Char name[50];
Puts(“Enter your name: “);
Gets(name);
Puts(salute);
Puts(name); }
Programming In C++, Lecture 7 By Umer Rana

18. Pointer to String Notation{
char *name[4]={
"Umer",
"Ali",
"Sarah",
"Adil" };
for(int i=0;i<4;i++)
printf("%s\n",name[i]); }
getch();
We use here instead of two dimensional String
char names[MAX][SIZE];
We use Pointer
char *name[4];
Pointer to string does not waste space between words.
Programming In C++, Lecture 7 By Umer Rana

19. Pointer to Pointer Notation
Pointers can be declared that point to other pointers. there is no limit to levels of indirection for a pointer type variable. An element of a two-dimensional array can be referenced with a pointer to a pointer.
int stud[4][2]={
{1,56},
{2,44},
{3,67},
{4,77} };
int i;
printf("\n Enterd Reg.No & Marks are");
for (i=0;i<=3;i++) {
printf("\n%d %d",*(*(stud+i)+0),*(*(stud+i)+1)); }
*(*(stud+i)+0) = stud[i][0]
*(*(stud+i)+1) = stud[i][1]
*(*(Row) + Colum)
Programming In C++, Lecture 7 By Umer Rana

20. Pointer to Pointer Notation
int ROWS=4;
Int COLS=5;
static int table [ROWS][COLS] = { {13,15,17,19,21},
{20,22,24,26,28},
{31,33,35,37,39},
{40,42,44,46,48} };
Int j,k;
For (j=0;j<ROWS;j++)
for (k=0;k<COLS; k++)
*(*table+j) + k) = *( *(table+j) +k) +10;
Printf(“\n”);
For (j=o;j<ROWS;j++) {
for (k=0;k<COLS;k++)
printf(“%d”, *( *(table+j) +k) );
Printf(“\n”);} }
Programming In C++, Lecture 7 By Umer Rana

21. Quiz Q.1: which is correct way to define a pointer? int &ptr x ;
Q.2: In Expression int *ptr what has type int?
Int Type variable
The Address of ptr
The variable pointed to by ptr
Q.2: What statement is missing?
int j, *ptr;
*ptr=3;
Programming In C++, Lecture 7 By Umer Rana

22. Quiz Q.3 What will be the output? int arr[]={4,5,6}; int i;
for(int i=0;i<3;i++)
printf(“%d”,*(arr+i))
Q.4 What will be the output?
printf(“%d”, arr+i)
Programming In C++, Lecture 7 By Umer Rana

23. Quiz Q.5 What will be the output? int arr[]={4,5,6};
int i, j=10, *ptr,*ptr2;
ptr2=&j;
ptr=arr;
printf(“%d”,*ptr2);
for(int i=0;i<3;i++)
printf(“%d”,*ptr++)
Programming In C++, Lecture 7 By Umer Rana