Pointer:
- The pointer is a variable and it is used to hold the address of another variable.
- It is mainly used to allocate and De-allocate memory.
- Each variable has two attributes: Address and value.
- There are three elements in the pointer.
* Pointer initialization
* Pointer declaration
* Pointer accessing
data
Note:
- & is an address operator.
- * is the value operator for accessing pointer value.
- %u is format specifiers for storing addresses.
- A pointer data type is similar to the address of another variable data type.
Syntax for pointers:
Syntax
for initializing pointer:
Syntax
for initializing pointer:
Data_type * variable_name;
Syntax
for declaring pointer:
Pointer_varable=&address_of_another_vaiable;
Syntax
for accessing the data by using pointer:
*pointer_variable =value(depend on requirements);
Example program for if:
Output:
#include<stdio.h>
#include<stdio.h>
#include<conio.h>
void main()
{
int a=5,*p;//initialization
p=&a;//declaration
clrscr();
printf("\n Value
of a is %d",a);
printf("\n address
of a is %u",&a);
printf("\n p value is %d",*p);
printf("\n address of p is %u",&p);
*p=2+a;//accessing data
printf("\n Recent
p value is %d",*p);
printf("\n Recent
a value is %d",a);
getch();
}
Explanation:
Here using variable a is an int data type, the integer will have 2 bytes and hence the address of the next address element is
incremented by 2.
Pointers
and functions:
- The pointer can be used as arguments in a function. The arguments or parameters to the function are passed in two ways.
Call by value
Call by reference
- If you want to more detail about this topic, click the below link to learn this topic.
Array
of pointers:
- Array elements are always stored in consecutive memory locations according to the size of the array.
- The size of the data type with the pointer variable refers to depends on the data type pointed by the pointer.
- A pointer when incremented always points to a location after skipping the number of bytes required for the data type pointed toby it.
Example program array of pointers:
/* Program to sort a list of strings in alphabetical
order using array of pointers*/
/* Program to sort a list of strings in alphabetical
order using array of pointers*/
#include<stdio.h>
#include<conio.h>
#include<stdlib.h>
#include<string.h>
void reorder(int a, char *x[]);//pointer with function
void main()
{
int i,a=0;
char *x[20];//array of pointer
clrscr();
printf("\n Enter
each string on a separate line below.\n");
printf("\n Type \
'END\' when finished.\n");
//read
in the list of strings
do
{
x[a]=(char*) malloc(12
* sizeof (char));//allocate memory
printf("\n String
%d: ",a+1);
scanf("%s",x[a]);
}
while(strcmp(x[a++],"END"));
//function
calling to reorder in the list of
strings
reorder(--a,x);
printf("\n
Reordered List of Strings: \n");
//
display the reordered list of strings
for (i=0;i<a;++i)
printf("\n String
%d: %s",i+1,x[i]);
getch();
}
//
function definition
void reorder(int a,char *x[])
{
char *temp;//pointer
variable to initialize
int i,y;
//
Find lowest of all remaining strings
for(y=0;y<a-1;++y)
for (i=y+1;i<a;++i)
if
(strcmp(x[y],x[i])>0)// compare the
string for order
{
//interchanging
the two strings
temp=x[y];
x[y]=x[i];
x[i]=temp;
}
return;
}
Output:
Structure
of pointers:
- A pointer pointing to a structure is known as pointers.
Example program:
#include<stdio.h>
#include<stdio.h>
#include<conio.h>
struct book
{
int book_no,bcost;
char *bname[20];
};
void main()
{
struct book p[3],*ptr;
clrscr();
printf("\n Enter
three book of details....\n");
printf("\n Enter
Book number, Name and Cost...\n");
for
(ptr=p;ptr<p+3;ptr++)
scanf("%d%s%d",&ptr->book_no,ptr->bname,&ptr->bcost);
printf("\n
STRUCTURE OUTPUT\n");
ptr=p;
while(ptr<p+3)
{
printf("%5d\t%-20s\t%d\n",ptr->book_no,ptr->bname,ptr->bcost);
ptr++;
}
getch();
}
Output:
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