Cpr Transperencies - Ch 05 Pointers

Chapter no. 5 Pointers

Pointer Memory Cell

Address 0 1 2 3 . . . . . . . 65,535

Memory Organization

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By, Kute T. B. for CPR (FYIF) 2007-08

Chapter no. 5 Pointers

Pointer int quantity = 126; Variable

Quantity

Value

126 5000

Address

Representation of a Variable

Variable

Value

Quantity

126

P

Address 5000

5048

5000

Pointer Variable

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By, Kute T. B. for CPR (FYIF) 2007-08

Chapter no. 5 Pointers

Pointer

Pointer Constants

Pointer Values

Pointer Variables

Pointer

Pointer Constants: Memory addresses within a computer. Pointer Value: Value stored at the address. Pointer Variable: Pointer value can be stored in another variable.

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By, Kute T. B. for CPR (FYIF) 2007-08

Chapter no. 5 Pointers

Accessing address of the variable & -

‘Address of’ operator.

This unary operator is used to obtain address of a variable and can only be used with single variable or single array element. It can not be used with constants, whole array or expressions.

Example: void main( ) { int a; char d; float k; a = 10; d = ‘J’; k = 15.23; printf(“Address of %d is %u”, a, &a); printf(“Address of %c is %u”, d, &d); printf(“Address of %f is %u”, k, &k); }

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By, Kute T. B. for CPR (FYIF) 2007-08

Chapter no. 5 Pointers

Declaring pointer variables data_type

*ptr_name;

This tells compiler three things about the variable ptr_name:

1. * tells that the variable ptr_name is a pointer variable. 2. ptr_name needs a memory location. 3. ptr_name points to a variable of type data_type. Example: int *p;

/*integer pointer */

float *x;

/* float pointer */

P

?

?

Contains Garbage

Points to Unknown location -5-

By, Kute T. B. for CPR (FYIF) 2007-08

Chapter no. 5 Pointers

Pointer Declaration Style int* p; int *p; int * p;

/* Style 1*/ /* Style 2*/ /* Style 3*/

Multiple Declarations: int *p, x, *q; Initialization of Pointer Variables Example: int quantity; int *p; p = &quantity;

/*Declaration*/ /*Initialization*/

or int *p = &quantity;

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By, Kute T. B. for CPR (FYIF) 2007-08

Chapter no. 5 Pointers

Pointers Flexibility int x, y, z, *p; ...... p = &x; ...... p = &y; ...... p = &z; ......

int x;

x

y

z

p

p1

p2

p3

int *p1 = &x; int *p2 = &x; int *p3 = &x;

x

......... .........

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By, Kute T. B. for CPR (FYIF) 2007-08

Chapter no. 5 Pointers

Accessing variable through pointer

* -

Indirection operator or Dereferencing operator.

We can call it ‘Contents of’. Example: int marks, *p, n; marks = 79; p = &marks; n = *p; ------------------------------p = &marks; n = *p; Equivalent to: n = *&marks; -8-

By, Kute T. B. for CPR (FYIF) 2007-08

Chapter no. 5 Pointers

Chain of Pointers Address2

p2

Address1

p1

Value

Variable

Multiple Indirections void main( ) { int x, *p1, **p2; x = 100; p1 = &x; p2 = &p1; printf(“Value : %d”,**p2); }

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By, Kute T. B. for CPR (FYIF) 2007-08

Chapter no. 5 Pointers

Pointer Expressions y = *p1 * *p2; sum = sum + *p3; z = 5 - *p2/ *p1; *p2 = *p1 + 10; p1++; -p2; sum += *p2; We may not use pointers in Division / Multiplication i.e. p1 / p2 or p1 * p2 or p1 / 3 Similarly, two pointers can not be added. i.e. p1 + p2 is not allowed.

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By, Kute T. B. for CPR (FYIF) 2007-08

Chapter no. 5 Pointers

Pointers and Arrays int x[5] = {8, 4, 9, 6, 3};

Elements

Value Address

X[0]

X[1]

X[2]

X[3]

8

4

9

6

3

1000

1002

1004

1006

1008

X[4]

Assigning the array to pointer: int *p; p = x;

or

p = &x[0];

Now, we can access every value of x using p++ to move from one element to another. - 11 -

By, Kute T. B. for CPR (FYIF) 2007-08

Chapter no. 5 Pointers

Pointers and Arrays #include<stdio.h> void main( ) { int *p, i; int array[5] = {8, 9, 6, 3, 2}; p = array; for(i=0; i<5; i++) { printf(“\n %d”,*p); //1 p++;

//2

} } 1

printf(“\n %d”,*(p+i));

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By, Kute T. B. for CPR (FYIF) 2007-08