1. POINTERS

2. Outline Introduction Pointer Variable Definitions and Initialization
Pointer Operators
Calling Functions by Reference

3. Introduction
Pointer is the address(i.e. a specific memory location) of an object
It can refer to different objects at different times
Pointers are used in C programs for a variety of purposes:
To return more than one value from a function(using pass by reference)
To create and process strings
To manipulate the contents of arrays and structures

4. Pointer Variable Definitions and Initialization
Pointer variables
Contain memory addresses as their values
Normal variables contain a specific value (direct reference)
Pointers contain address of a variable that has a specific value (indirect reference)
Indirection – referencing a pointer value
num 7
num 7
numPtr

5. Pointer Variable Definitions and Initialization
Pointer definitions
* used with pointer variables
int *numPtr;
Defines a pointer to an int (pointer of type int *)
Multiple pointers require using a * before each variable definition
int *numPtr1, *numPtr2;
Can define pointers to any data type
Initialize pointers to 0, NULL, or an address
0 or NULL – points to nothing (NULL preferred)
int *numPtr = NULL; OR int *numPtr = 0;

6. Pointer Operators Symbol & is called address operator
Returns address of operand
int num = 7;
int *numPtr;
numPtr = # /* numPtr gets address of num */
numPtr “points to” num
numPtr
num 7
500000
600000
Address of num is value of numPtr

7. Pointer Operators
Symbol * is called indirection/dereferencing operator
Returns a synonym/alias of what its operand points to
*numPtr returns num (because numPtr points to num)
* can also be used for assignment
Returns alias to an object
*numPtr = 10; /* changes num to 10 */ show pictures!!
Dereferenced pointer (operand of *) must be an lvalue (no constants)
* and & are inverses
They cancel each other out

8. Sample program *numPtr = 15; number = 7
numPtr points to num whereby the value is = 7
Address of numPtr : Contents of numPtr :
Address of num :
Dereferencing pointer, *numPtr = 15
num = 20
*numPtr = 20
*numPtr + num1 = 25
#include <stdio.h>
int main()
{ int num;
int *numPtr;
int num1=5;
num = 7;
printf("number = %d\n", num);
numPtr = &num;
printf("numPtr points to num whereby the value is = %d\n",*numPtr);
printf("Address of numPtr : %d Contents of numPtr : %d\n", &numPtr, numPtr);
printf("Address of num : %d\n\n", &num);
*numPtr = 15;
printf("Dereferencing pointer, *numPtr = %d\n", *numPtr);
num = num + num1;
printf(“num = %d\n”, num);
printf("*numPtr = %d\n", *numPtr);
printf("*numPtr + num1 = %d\n", *numPtr + num1);
return 0; }

9. Calling Functions by Reference
Call by reference with pointer arguments
Pass address of argument using & operator
Allows you to change actual location in memory
Arrays are not passed with & because the array name is already a pointer
* operator
Used as alias/nickname for variable inside of function
void fun1( int *number ) {
*number = 2 * ( *number ); }
*number used as nickname for the variable passed

10. Enter character : f
Do you want to continue?y
Enter character : I
Enter character : k
Do you want to continue?n
Number of vowel : 1
Number of consonant : 2
Remember..last time
#include <stdio.h>
#include <string.h>
char read();
void find_count_vc(char, int*, int*);
void print(int,int);
int main()
{ char ch, choice; int count_v=0,count_c=0; do
{ ch = read();
find_count_vc(ch, &count_v, &count_c);
printf("Do you want to continue?");
scanf("%c", &choice);
getchar();
}while((choice == 'y') ||(choice =='Y'));
print(count_v,count_c);
return 0; }
char read()
{ char ch1;
printf("Enter character : ");
scanf("%c", &ch1);
return(ch1);
void find_count_vc(char ch1, int *vowel, int *consonant) {
switch(ch1)
{ case 'A':
case 'a':
case 'E':
case 'e':
case 'I':
case 'i':
case 'O':
case 'o':
case 'U':
case 'u': *vowel = *vowel +1;break;
default: *consonant = *consonant + 1; }
void print(int vowel, int consonant)
printf("Number of vowel : %d\n", vowel);
printf("Number of consonant : %d\n", consonant);
Functions that “return” more than one value i.e. arguments are passed by ref