Thread: code doesnt flip array

why doesnt this code flip the array and print the result??

Code:

#include<stdio.h>
#include<stdlib.h>

main()
{
	int b[5]={10,20,30,40,50};
	int *frontp, *backp;
	int hold;
	int i;

	for(i=0;i<5;i++)printf("%d^",b[i]);

	frontp=&b[0];
	backp=&b[4];

	while(frontp < backp)
	{
		hold=*frontp;
		*frontp=*backp;
		*backp=hold;

		frontp=&b[1];
		backp=&b[3];
	}

	for(i=0;i<5;i++)printf("%d^",b[i]);

	return 0;
}

this compares pointers (addresses).

while(frontp < backp)

this will not always return the right results. you want to compare whats being pointed to, like this:

Code:

	while(*frontp < *backp)

This is basically what your code is doing:

Code:

int front = 0;
int back = 4;

while (front < back)
{
   ...
   front = 1;
   back = 3;   
}

You can use ++ and -- to move a pointer to the next/previous element in an array. (ie frontp++ backp--)
Do that and your loop will work, and on any size array.

gg

You don't need pointers to flip the array, much easier would be to use just the index. The first element is 0, the last element is N-1. The second element is 1, the element to switch with is N-2. Etc. Or use two index variables and let one start at 0 and the other at N-1.