Need Help, Bubblesort in pointer

[banowati]

I have assignment to complete the following coding. My lecturer only give the number of rows and the variables used. I was asked to fill out the program itself, to sort the data using the bubble sort and then find the median value. This program uses a pointer, and I am still confused to use it. I've tried but still not working. I think my mistake was laying of variabel *x in the main. Please help me, where is my mistake? thank you very much :)

  #include <iostream>
#include <cstdlib>
#include <iomanip>
#define max 10

using namespace std;

void swap(int *x, int *y){
	int t;
	if(*x > *y){
		t = *x;
		*x = *y;
		*y = t;
	}
}

void bubblesort (int *array, int size){
	for(int k=1; k<size; k++){
		for(int l=(size-1); l>=k; l--){
			if (array[l]<array[l-1])
			swap(&array[l],&array[l+1]);
		}
	}
}

void median(int *array, int size){
	*array = array[size/2];
}

int main(){
	int *x;
	int qty;
	
	cout<<"The number of data to be entered? ";
	cin>>qty;
	
	cout<<"Enter data\n";
	
	for(int i=1; i<=qty; i++){
		cout<<"Numbers - "<<i<<" : ";
		cin>>*x;
	}
	
	cout<<"Data before sorted : "<<endl;
	for(int i=1; i<qty; i++);
	{
		cout<<setw(4)<<*x;
	}
		
	bubblesort(x,qty);
	cout<<endl;	
	cout<<"Sorting in ascending"<<endl;
	for (int i=1; i<qty; i++);
	{
		cout<<setw(4)<<*x;
	}
	
	cout<<endl;
	
	cout<<"Median value : "<<median<<endl;
	return 0;
}

[keskiverto]

int * x;
*x = 42;

Yes, this is an error. Variable of type pointer holds a memory address. Dereferencing a pointer accesses the value in the memory in the address that the pointer has. In this short example line 1 creates a pointer variable but does not set its value. The x does not hold any valid address. Then, in line 2 we try to write 42 into the memory location that we have no idea about.

Your swap and bubblesort do both test val1 < val2. Are you sure that is appropriate and logical?

Your median is equivalent to:

void median(int *array, int size){
	array[0] = array[size/2];
}

That is not what one expects from such function. How about returning a value from that function?

It is not clear, which parts of your code have been written by your lecturer and what is your contribution.

[banowati]

Oh.. yes. I think I make mistake for swap and bubblesort.

It is the task from my lecturer.

#include <iostream>
#include <cstdlib>
#include <iomanip>
#define max 10

using namespace std;

void swap(int *x, int*y)
{
	…………………………………;
	if (…………………………………)
	{
		…………………………………;
		…………………………………;
		…………………………………;
	}
}

void bublesort (int *array, int size)
{
	for (…………………………………)
	{
		for(…………………………………)
		{
			…………………………………
				…………………………………
		}
	}
}

void ……………………………;
{
	……………………………;
}

int main()
{
	
	int *x; 
	int ……; //var for the number of data entered

	
	cout << "The number of data to be entered? ";
	cin >> ……………………………;

	
	cout << "Enter data\n";
	……………………………
	{
		……………………………;
		cin >> ……………………………;;
	}
	
        //show the data 
	cout<<"Data before sorted : "<<endl;
	……………………………;
	{
		……………………………;
	}
	
        //call sort function
	……………………………;
	
	cout<<endl;
	
        cout<<"Sorting in ascending"<<endl;
	……………………………;
	{
		……………………………;;
	}
	
	cout<<endl;


        //call median function
	……………………………;
		
	return 0;
}

He only give *x as a variable that holds the number.

I'm not sure I'm allowed to add another variable. If it should stay that way, then how?

[keskiverto]

That does give the impression that the main() should allocate memory dynamically for the array, but there are no placeholders for the new and corresponding delete [].

The median function does not return a value. Therefore, it ought to show the median. Btw, if 'size' is even, then http://en.wikipedia.org/wiki/Median

I have a feeling that the condition in swap() is to prevent swap of item with itself.