Reverse the content of array using pointer at variable location

In this program,two pointers ptr1 and ptr2 are used to reverse the content of array a. The data is saved at specific memory location using pointer instead of saving it in array.After saving the data ptr1 points at first memory location and ptr2 points at last menory location. The values are swaaped using while loop until the ptr1 is less than ptr2.Temporary variable t is used for holding the value temporarily.At the end of while loop,the values gets saved in reverse order.

#include < stdio.h >
#include < conio.h > 
#include < alloc.h >

void main()
{
	int a[20],*ptr1,*ptr2,n,t;
	clrscr();
	printf("\nEnter n");
	scanf("%d",&n);
	//read n numbers
	printf("\nEnter %d numbers \n",n);
	for(ptr1=a;ptr1<=a+n-1;ptr1++)
	{
		scanf("%d",ptr1);
	}
	//reverse the order of n numbers
	ptr1=a; //initialize ptr1 to first number
	ptr2=a+n-1;//initialize ptr2 to last number
	while(ptr1 < ptr2)
	{
		t=*ptr1;
		*ptr1=*ptr2;
		*ptr2=t;
		ptr1++;
		ptr2--;
	}
	printf("\n The resultant array is \n");
	for(ptr1=a;ptr1<=a+n-1;ptr1++)
	{
		printf("%4d",*ptr1);
	}
}