This C++ program contains implementation of Mergesort, Heapsort and Quicksort in a single class.I used template for defining set of numbers to sort so the class can be used to sort any type of numeric values. I have also given a main function which utilizes this class for sorting a set of numbers.

Logic of these sorting algorithms can be found in Fundamentals of Data Structures book by Ellis Horowitz and Sartaj Sahni.

#include<iostream.h>
#include<conio.h>
#define LIST_SIZE 30
template <class R>
class Sort
{
      private:
      void Merge(R a[],int f,int s,int t)
      {
            R b[LIST_SIZE];
            int i=f,j=s+1,k=0;
            while((i<=s)&&(j<=t))
            {
                  if(a[i]<a[j])
                  {
                        b[k]=a[i];
                        i++;
                  }
                  else
                  {
                        b[k]=a[j];
                        j++;
                  }
                  k++;
            }
            while(i<=s)
            {
                  b[k]=a[i];
                  i++;
                  k++;
            }
            while(j<=t)
            {
                  b[k]=a[j];
                  j++;
                  k++;
            }
            k--;
            j=0;
            for(i=f;i<=t;i++)
            {
                  a[i]=b[j];
                  j++;
            }
      }
      void Heap(R x[], int n, int k)
      {
            int j;
            R t;
            if((2*k+2<n)&&(x[2*k+2]>x[2*k+1])) j=2; else j=1;
            if(x[2*k+j]>x[k])
            {
                  t=x[2*k+j];
                  x[2*k+j]=x[k];
                  x[k]=t;
            }
      }
      public:
      void MergeSort(R x[],int m,int n)
      {
            int q;
            if(m<n)
            {
                  q=(m+n)/2;
                  MergeSort(x,m,q);
                  MergeSort(x,q+1,n);
                  Merge(x,m,q,n);
            }
      }
      void HeapSort(R x[], int n)
      {
            R t;
            if(n>1)
            {
                  for(int i=n/2-1;i>=0;i--)
                        Heap(x,n,i);
                  t=x[0];
                  x[0]=x[n-1];
                  x[n-1]=t;
                  HeapSort(x,n-1);
            }
      }
      void QuickSort(R x[],int m,int n)
      {
            R k,t;
            int i,j;
            if(m<n)
            {
                  k=x[m];
                  i=m;
                  j=n+1;
                  do
                  {
                        do{ i++; }while(x[i]<k);
                        do{ j--; }while(x[j]>k);
                        if(i<j)
                        {
                              t=x[i];
                              x[i]=x[j];
                              x[j]=t;
                        }
                  }while(i<j);
                  x[m]=x[j];
                  x[j]=k;
                  QuickSort(x,m,j-1);
                  QuickSort(x,j+1,n);
            }
      }
}
void main()
{
      int g[LIST_SIZE],n,i;
      Sort<int> M;
      char c;
      do
      {
            clrscr();
            cout<<"Menu..."<<endl<<"1.Quick Sort"<<endl;
            cout<<"2.Heap Sort"<<endl<<"3.Merge Sort"<<endl;
            cout<<"4.Exit"<<endl<<"Enter your choice: ";
            c=getche();
            switch(c-48)
            {
                  case 1: case 2: case 3:
                  cout<<endl<<"How many Numbers: ";
                  cin>>n;
                  cout<<"Enter Numbers..."<<endl;
                  for(i=0;i<n;i++) cin>>g[i];
            }
            switch(c-48)
            {
                  case 1: M.QuickSort(g,0,n-1); break;
                  case 2: M.HeapSort(g,n); break;
                  case 3: M.MergeSort(g,0,n-1);
            }
            switch(c-48)
            {
                  case 1: case 2: case 3:
                  cout<<"Sorted Numbers..."<<endl;
                  for(i=0;i<n;i++)
                        cout<<endl<<g[i];
                  getch();
            }
      }while(c-48!=4);
}