Pointers in C

* pointer 
     A pointer is a variable which is used to store address of another variable.
     The syntax of pointer variable declaration is as follows:
                      datatype *pointer variable name
eg: let 
         int a=10;                     //&a=99;
         int *p=&a;
         *p=99;
             |> change the value at the address of  P.

* if we want to modify 'a' value from 10 to 99. we have to write a=99 to do this.
             
But we can also modify 'a'  variable without accessing it directly. This can be done with the help of the pointer variable  p.
          
The statement *p=99 means change the value at the address of p to 99.
          
By this way 'a' value becomes 99 without modifying directly, with the help of pointer variable.

/* C Program to swap 2 value using call by value and call by address */     By Amit raj purohit
http://codevidyalay.blogspot.com

#include<stdio.h>
void swapvalue(int,int);
void swapaddress(int*,int*);
int main()
{

int a=100,b=30;
printf("a and b values before swapping %d %d",a,b);

swapvalue(a,b);
printf("\na and b values after call by value %d %d",a,b);

swapaddress(&a,&b);
printf("\na and b values after call by address %d %d",a,b);
return 0;
}

void swapvalue(int a,int b)
{
int c;
c=a;
a=b;
b=c;
}
void swapaddress(int *p,int *q)
{
int c;
c=*p;
*p=*q;
*q=c;
}

INPUT/OUTPUT:
a and b values before swapping 100 30
a and b values after call by value 100 30
a and b values after call by address 30 100