bubble sort via pointer

[mw3284]

I'm trying to do a basic bubble sort using dynamic memory allocation and pointers within a class. I have tested the getRain() function, it returns 0.26 and 1.1. After I call my sort function and display again it is the same as my unsorted display. Thank you for your consideration.

#include <iostream>
#include <iomanip>
#include "rainfall.h"
using namespace std;

void fill(Rainfall *p);
void sort(Rainfall *p);

int main()
{	Rainfall *p = new Rainfall[10];
	fill(p);
	cout << "Rainfall:   Date:\n";
	for(int i = 0; i < 10; i++)
	{	(p + i) ->displayRainfall();
		cout << setw(8) << " ";
		(p + i) ->displayDate();
		cout << endl;
	}

	cout << "\nSort in descending order? (Y/N) ";
	char choice;
	cin >> choice;
	if(choice == 'y' || choice == 'Y')
	{	sort(p);  //********
		cout << "Rainfall:   Date:\n";
		for(int i = 0; i < 10; i++)
		{	(p + i) ->displayRainfall();
			cout << setw(8) << " ";
			(p + i) ->displayDate();
			cout << endl;
		}}
	
	delete [] p;
	p = 0;
	return 0;
}

/******************************************************************/
//setData(rainfall, month, day, year)
void fill(Rainfall *p)
{	p ->setData(0.26, 10, 11, 2011);
	(p + 1) ->setData(1.1, 10, 8, 2011);
	(p + 2) ->setData(0, 10, 7, 2011);
	(p + 3) ->setData(0.61, 10, 6, 2011);
	(p + 4) ->setData(0, 10, 5, 2011);
	(p + 5) ->setData(0.22, 10, 4, 2011);
	(p + 6) ->setData(1.11, 10, 1, 2011);
	(p + 7) ->setData(0, 9, 30, 2011);
	(p + 8) ->setData(0.58, 9, 29, 2011);
	(p + 9) ->setData(0.89, 9, 28, 2011);
}

/******************************************************************/
void sort(Rainfall *p)
{	int num = (10 - 1);
	for(int r = 0; r < num; num--)
		{for(int i = 0; i < num; i++)
			{if(p->getRain() > (p + 1)->getRain())
				{	Rainfall temp = *p;
					*p = *(p + 1);
					*(p + 1) = temp;
				}}}}

[ne555]

[code] "Please use code tags" [/code]

//this two are equivalent
(p+i)->something();
p[i].something();

//if(p->getRain() > (p + 1)->getRain())
if( p[0].getRain() > p[1].getRain() )

When passing arrays to function, use one of the followings:
_A terminate value (that doesn't appear anywhere on the array). By instance '\0' with cstrings.
_Pass the dimension as an extra parameter
_Pass two pointers in range [) (close-open)

[mw3284]

One of the stipulations of the assignment was to leave out any array subscripts.

[Zhuge]

leave out any array subscripts

Oh for the love of...
That is rather stupid in my opinion, but whatever.

Anyway, the problem is in your algorithm. Your comparison only compares p[0] and p[1] ever. I assume you wanted to use p[r] and p[i] in there somewhere?

[mw3284]

The problem remains with:

if((p + i)->getRain() > (p + i + 1)->getRain())
{	Rainfall temp = *p;
	*p = *(p + 1);
	*(p + 1) = temp;
}

[ne555]

//	Rainfall temp = *p;
//	*p = *(p + 1);
//	*(p + 1) = temp;

swap( p[0], p[1] );

[D80DSL3A]

Make the same changes to lines 2, 3 and 4 that you made to line 1. Note: p and (p+1) are pointing to only the first 2 array elements. Your code just swaps these first 2 elements back and forth repeatedly. You should be working with *(p+i) and *(p+i+1) throughout.

[mw3284]

Thanks:

if((p + i)->getRain() < (p + i + 1)->getRain())
{	Rainfall temp = *(p + i);
	*(p + i) = *(p + i + 1);
	*(p + i + 1) = temp;
}