Thread: sorting - merge -

Program doesnt return to main after calling merge sort. Could someone point out why is that?

Code:

private:
	int nNumItems;
	string *pasWords;
....more code
....
int MergeSort();
int gMergeSort(string*pasWords, int nStart, int nEnd);
int Merge(string*pasWords, int nStart, int nMidpoint, int nEnd);

Code:

int Wordlist::MergeSort()
{
	int nStart=0, nEnd=nNumItems-1;

	if (pasWords == NULL)
	{
		cout << "Array is Empty..." << endl;
		return 0;
	}
	gMergeSort(nStart, nEnd );
	return 0;
}


int Wordlist::gMergeSort(int nStart, int nEnd)
{
	int nMidpoint=0;
	
	if (nEnd >= nStart+1)
	{
		nMidpoint = (nEnd-nStart)/2;					//Getting Midpoint
		gMergeSort(nStart, nMidpoint);
		gMergeSort(nMidpoint+1, nEnd);
		Merge(nStart, nMidpoint, nEnd);
	}
	
	return 0;
}

int Wordlist::Merge(int first, int mid, int last)
{
	int i,j,k;
	string *temp;
	temp = new string [(nNumItems-1)/2];  

	i=0, k=first;
	while(k<=mid)
		temp[i++]=pasWords[k++];

	i=0,j=mid+1,k=first;
	for(;;)
	{
		if(temp[i]<= pasWords[j])
		{
			pasWords[k++]=temp[i++];
			if(i>mid-first) return 0;
		}
		else
		{
			pasWords[k++]=pasWords[j++];
			if(j>last) break;
		}
	}
	while(i<=mid-first)
		pasWords[k++]=temp[i++];

	return 0;
}

after the red marked call to function, i tried putting a cout, but it just skips it and teriminates the program without going back to main.

after the red marked call to function, i tried putting a cout, but it just skips it and teriminates the program without going back to main.

How does your program terminate? Does it get stuck in an infinite loop?

I also think you could organize your program differently. All the sort functions can be called by your object in main() and then return to main() when they are done. main() is supposed to be the air traffic controller. Instead, you are calling a function from main(), then jumping from inside that function to another function, and then doing it again, which is a mess to troubleshoot.

I envision something like this:

Code:

int main()
{

    WordList myList;
    ....
    myList.MergeSort();
	
    myList.gMergeSort(0); //the 2nd param nNumItems can be accessed from inside gMergeSort()
	
    myList.Merge(1, 2, 3);

normally... but it is not suppose to terminate.