tack around the variable 'a' was corrupted

[PK Dey]

Error>> Run-Time Check Failure #2 - Stack around the variable 'a' was corrupted.

Could someone please explain Why the above error occurs when I run the following code?

  #include <iostream>
using namespace std;
void quicksort(int[], int, int);
int partitioning(int[], int, int);
int main()
{
	int a[9], b[9], c[9], d[9], i, j = 0, k;
	for (k = 0; k < 4; ++k)
	{
		if (k == 0) cout << "Enter the elements of array A: ";
		if (k == 1) cout << "Enter the elements of array B: ";
		if (k == 2) cout << "Enter the elements of array C: ";
		if (k == 3) cout << "Enter the elements of array D: ";
		for (i = 0; i < 9; ++i)
		{
			if (k == 0) cin >> a[i];
			else if (k == 1) cin >> b[i];
			else if (k == 2) cin >> c[i];
			else cin >> d[i];
		}
	}
	for (k = 0; k < 4; ++k)
	{
		if (k == 0) cout << "Elements of array A Before     Quick sorting: ";
		if (k == 1) cout << "Elements of array B before Insertion sorting: ";
		if (k == 2) cout << "Elements of array C before     Shell sorting: ";
		if (k == 3) cout << "Elements of array D before     Merge sorting: ";
		for (i = 0; i < 9; ++i)
		{
			if (k == 0) cout << a[i] << " ";
			else if (k == 1) cout << b[i] << " ";
			else if (k == 2) cout << c[i] << " ";
			else cout << d[i] << " ";
		}
		
		if(k==0) quicksort(a, 0, 9);
		if(k==1) quicksort(b, 0, 9);
		if(k == 2) quicksort(c, 0, 9);
		if (k == 3) quicksort(d, 0, 9);
		if (k == 0) cout << "Elements of array A After     Quick sorting: ";
		for (i = 0; i < 9; ++i)
		{
			if (k == 0) cout << a[i] << " ";
		}
		cout << '\n';
	}
}
void quicksort(int a[], int l, int h)
{
	int u;
	if (l < h)
	{
		u = partitioning(a, l, h);
		quicksort(a, l, u - 1);
		quicksort(a, u + 1, h);
	}
}
int partitioning(int a[], int i, int j)
{
	int pivote=0, temp=0, k=0;
	pivote = a[i]; k = i;
	do
	{
		do ++i; while (a[i] < pivote);
		while (a[j] > pivote) j--;
		if (i < j)
		{
			temp = a[i];
			a[i] = a[j];
			a[j] = temp;
		}
	} while (i < j);
	a[k] = a[j];
	a[j] = pivote;
	return(j);
}

[dutch]

It means you're writing outside of the array. You need to pass the highest offset in the array as the last argument to quicksort, not the size of the array.

#include <iostream>
using namespace std;

void quicksort(int[], int, int);
int partitioning(int[], int, int);

int main()
{
    const int NumArrays{4}, Size{9};
    int a[NumArrays][Size]
    {
        { 5, 4, 2, 9, 7, 1, 3, 6, 8 },
        { 1, 3, 6, 8, 5, 4, 2, 9, 7 },
        { 8, 5, 4, 2, 1, 3, 6, 9, 7 },
        { 9, 7, 1, 3, 6, 5, 4, 2, 8 },
    };
/*
    for (int k = 0; k < NumArrays; ++k)
    {
        cout << "Enter the elements of array " << char('A' + k) << ": ";
        for (int i = 0; i < Size; ++i) cin >> a[k][i];
    }
*/
    for (int k = 0; k < NumArrays; ++k)
    {
        cout << "Elements of array " << char('A' + k) << " before sorting: ";
        for (int i = 0; i < Size; ++i) cout << a[k][i] << ' ';
        cout << '\n';
        quicksort(a[k], 0, Size - 1);
        cout << "Elements of array " << char('A' + k) << " after sorting : ";
        for (int i = 0; i < Size; ++i) cout << a[k][i] << ' ';
        cout << '\n';
    }
}

void quicksort(int a[], int l, int h)
{
    if (l < h)
    {
        int u = partitioning(a, l, h);
        quicksort(a, l, u - 1);
        quicksort(a, u + 1, h);
    }
}

int partitioning(int a[], int i, int j)
{
    int pivote = a[i], k = i;
    do
    {
        do ++i; while (a[i] < pivote);
        while (a[j] > pivote) j--;
        if (i < j) swap(a[i], a[j]);
    } while (i < j);
    a[k] = a[j];
    a[j] = pivote;
    return j;
}

[PK Dey]

Thanks dutch! I have learned a lot of key points of C++ language from your replay! Manny Manny thanks again!