array type int not assignable

Question

Hello,

How can I fix this error? I want to assign n from parameter.

#include <iostream> 
using namespace std;


void merge(int gArray[], int low, int mid1,
	int mid2, int high, int destArray[])
{
	int i = low, j = mid1, k = mid2, l = low;

	// choose smaller of the smallest in the three ranges  
	while ((i < mid1) && (j < mid2) && (k < high))
	{
		if (gArray[i] < gArray[j])
		{
			if (gArray[i] < gArray[k])
			{
				destArray[l++] = gArray[i++];
			}
			else
			{
				destArray[l++] = gArray[k++];
			}
		}
		else
		{
			if (gArray[j] < gArray[k])
			{
				destArray[l++] = gArray[j++];
			}
			else
			{
				destArray[l++] = gArray[k++];
			}
		}
	}

	// case where first and second ranges 
	// have remaining values  
	while ((i < mid1) && (j < mid2))
	{
		if (gArray[i] < gArray[j])
		{
			destArray[l++] = gArray[i++];
		}
		else
		{
			destArray[l++] = gArray[j++];
		}
	}

	// case where second and third ranges 
	// have remaining values  
	while ((j < mid2) && (k < high))
	{
		if (gArray[j] < gArray[k])
		{
			destArray[l++] = gArray[j++];
		}
		else
		{
			destArray[l++] = gArray[k++];
		}
	}

	// case where first and third ranges have  
	// remaining values  
	while ((i < mid1) && (k < high))
	{
		if (gArray[i] < gArray[k])
		{
			destArray[l++] = gArray[i++];
		}
		else
		{
			destArray[l++] = gArray[k++];
		}
	}

	// copy remaining values from the first range  
	while (i < mid1)
		destArray[l++] = gArray[i++];

	// copy remaining values from the second range  
	while (j < mid2)
		destArray[l++] = gArray[j++];

	// copy remaining values from the third range  
	while (k < high)
		destArray[l++] = gArray[k++];
}


/* Performing the merge sort algorithm on the
given array of values in the rangeof indices
[low, high). low is minimum index, high is
maximum index (exclusive) */
void mergeSort3WayRec(int gArray[], int low,
	int high, int destArray[])
{
	// If array size is 1 then do nothing  
	if (high - low < 2)
		return;

	// Splitting array into 3 parts  
	int mid1 = low + ((high - low) / 3);
	int mid2 = low + 2 * ((high - low) / 3) + 1;

	// Sorting 3 arrays recursively  
	mergeSort3WayRec(destArray, low, mid1, gArray);
	mergeSort3WayRec(destArray, mid1, mid2, gArray);
	mergeSort3WayRec(destArray, mid2, high, gArray);

	// Merging the sorted arrays  
	merge(destArray, low, mid1, mid2, high, gArray);
}

void mergeSort3Way(int gArray[], int n)
{
	// if array size is zero return null  
	if (n == 0)
		return;

	// creating duplicate of given array  
	int fArray[n];

	// copying alements of given array into  
	// duplicate array  
	for (int i = 0; i < n; i++)
		fArray[i] = gArray[i];

	// sort function  
	mergeSort3WayRec(fArray, 0, n, gArray);

	// copy back elements of duplicate array  
	// to given array  
	for (int i = 0; i < n; i++)
		gArray[i] = fArray[i];
}

// Driver Code 
int main()
{
	int data[] = { 45, -2, -45, 78, 30,
				 -42, 10, 19, 73, 93 };
	mergeSort3Way(data, 10);
	cout << "After 3 way merge sort: ";
	for (int i = 0; i < 10; i++)
	{
		cout << data[i] << " ";
	}
	return 0;
}

Answer 1

Try fixing the error at line 124. For example:

 

#include <vector>

. . .

void mergeSort3Way( int gArray[], int n )

{

       // if array size is zero, return 

       if( n == 0 )

             return;

 

       // creating duplicate of given array 

       vector<int> duplicate( gArray, gArray + n );

 

       // sort function 

       mergeSort3WayRec( duplicate.data(), 0, n, gArray );

 

       // copy back elements of duplicate array 

       // to given array 

       for( int i = 0; i < n; i++ )

             gArray[i] = duplicate[i];

}

Answer 2

Hello,

the compiler must know the size of the array at compile time. To define an array at runtime, use new[].

void mergeSort3Way(int gArray[], int n)
{
	// if array size is zero return null  
	if (n == 0)
		return;

	// creating duplicate of given array  
	int *fArray = new int[n];
        if (!fArray) return; // error

	// copying alements of given array into  
	// duplicate array  
	for (int i = 0; i < n; i++)
		fArray[i] = gArray[i];

	// sort function  
	mergeSort3WayRec(fArray, 0, n, gArray);

	// copy back elements of duplicate array  
	// to given array  
	for (int i = 0; i < n; i++)
		gArray[i] = fArray[i];

        delete[] fArray;
}

Regards, Guido

Answer 3

	// copy back elements of duplicate array  
	// to given array  
	for (int i = 0; i < n; i++)
		gArray[i] = fArray[i];

Since "mergeSort3WayRec" will write its results into gArray, isn't it rather counterproductive to overwrite that with your copy of the original input data?

---

Tim Roberts | Driver MVP Emeritus | Providenza &amp; Boekelheide, Inc.