Sort Not working

[mqueene7]

below is my code - i can get the numbers to generate but they will not sort. i need to use the merge sort method for sorting. i also need to make this array size whatever the user wants - but it will have to go up to 1000000.

can someone point out why my numbers are not sorting? I've been testing with small values such as 4 or 5.

#include <iostream>
#include <cstdlib>
#include <cmath>
#include <time.h>
using namespace std;

int a[10], aSize;
void merge(int,int,int);
void merge_sort(int low, int high);

void merge_sort(int low, int high)
{ int mid, temp;
 if (low==high) //this works - checking if there's one element
	 return;
 if (low+1==high) // checking if there are only 2 elements
 {	 if (low>high) //compare the two elements
	{
		 temp=high; //swap if low is greater than high
		 high=low;
		low=temp;
	}
 }
 else 
	 if(low<high)
 {  
	 mid=(low+high)/2;
  merge_sort(low,mid);
  merge_sort(mid+1,high);
  merge(low,mid,high);
 }}
void merge(int low,int mid,int high)
{	int size, p, q, i; //, r;
	int c[10]; //array c - the temporary array for sorting
	size = high - low + 1; //size of array c
	c[size];
	p=low; //index for a[i]...a[mid]
	q=mid+1; //index for a[mid + 1]...a[j]
	while((p<=mid)&&(q<=high))
	{		if(a[p]<=a[q]) 
		{		c[i]=a[p]; //copy smaller value to local array c
				p++;
		  }
		else
		  {		c[i]=a[q];
				q++;
		  }
	  i++;
	}
	while (a[p]<= mid)//copy the rest of the longer array
	{	 c[i] = a[p];
	}
	while (a[q]<=high)//copy the rest of the larger array
	 {	 c[i]=a[q];
	 }
	for (i=low; i<=high; i++)//copy back from temp array to main array
		{	 a[i]=c[i];
		 }}
int main()
{
	long timeElapsed;
	timeElapsed = clock();
	int i,elem;
	a[aSize];
	cout<<"*********************************************************************"<<endl;
	cout<<"                             MERGE SORT PROGRAM"<<endl;
	cout<<"**********************************************************************"<<endl<<endl<<endl;
	cout<<"Please Enter THE NUMBER OF ELEMENTS you want to sort[THEN PRESS ENTER]:"<<endl;
	cin>>aSize;
	for (i=0; i<aSize; i++)
	{	elem =((rand()*9)+1);
        cout<<endl<<"element "<<i<<"is "<<elem<<endl;
        a[i]= elem;
        cout<<"When i is "<<i<<" ai is "<<a[i];
    }
    merge_sort(0,aSize);
    cout<<endl<<"So, the sorted list (using MERGE SORT) will be : "<<endl;
    for(i=0;i<aSize;i++)
    {  cout<<a[i]<<" ";
    }
    cout<<endl<<endl<<"Time Elapsed is: "<<timeElapsed<<endl<<endl<<endl<<endl;
    system("PAUSE");
return 0;
}

[scruggsy]

void merge(int low,int mid,int high)
{	int size, p, q, i; //, r;
	int c[10]; //array c - the temporary array for sorting
	size = high - low + 1; //size of array c
	c[size];
	p=low; //index for a[i]...a[mid]
	q=mid+1; //index for a[mid + 1]...a[j]
	while((p<=mid)&&(q<=high))
	{		if(a[p]<=a[q]) 
		{		c[i]=a[p]; // <--- HERE"S YOUR PROBLEM

You never initialized i before using it to index into the c array.

[mqueene7]

You never initialized i before using it to index into the c array.

i is initialized in the first line

 int size, p, q, i;

[Ganon11]

Correction: i is declared (so it exists), but you never give it a value. Giving a starting value to a variable is called initializing it.

[scruggsy]

i is initialized in the first line

 int size, p, q, i;

Declared, not initialized.
Until you give it a value, i contains junk.
Your program will crash because c[i] tries to access memory outside of your array.