Merge Sort in C++

I wrote this program to ask the user to give how many items to be sorted and then the program will display the original and sorted arrangement of values using merge sort in C programming language.

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Sample Program Output

Program Listing

merge.cpp

#include<iostream>

using namespace std;

int Merge(int A[],int p, int q,int r)     

{

int n1=q-p+1,i,j,k;       

int n2=r-q;               

int L[n1],R[n2];

for(i=0;i<n1;i++)

{

L[i]=A[p+i];

}

for(j=0;j<n2;j++)

{

R[j]=A[q+j+1];

}

i=0,j=0;

for(k=p;i<n1&&j<n2;k++)

{

if(L[i]<R[j])

{

A[k]=L[i++];

}

else

{

A[k]=R[j++];

}

}

while(i<n1)            

{

A[k++]=L[i++];

}

while(j<n2)            

{

A[k++]=R[j++];

}

}

int MergeSort(int A[],int p,int r)   

{

int q;                                

if(p<r)

{

q=(p+r)/2;                     

MergeSort(A,p,q);

MergeSort(A,q+1,r);

Merge(A,p,q,r);

}

}

int main()

{

int A_Size=0;                          

cout <<"\n\n";

    cout <<"\tMerge Sort in C++";

    cout <<"\n\n";

cout<<"\tHow many elements? :";

cin>>A_Size;

int A[A_Size];

for(int i=0;i<A_Size;i++)

{

cout <<"\tEnter value on element no. " <<i+1 << " : ";

cin>>A[i];

}

    cout<<"\n\n";

cout <<"\tOriginal Arrangement";

cout<<"\n\n";

cout <<"\t";

for(int i=0;i<A_Size;i++)

{

cout<<" " <<A[i]<<" ";

}

cout<<"\n\n";

cout <<"\tSorted Arrangement";

cout<<"\n\n";

cout <<"\t";

MergeSort(A,0,A_Size-1);

for(int i=0;i<A_Size;i++)

{

cout<<" "<<A[i]<<" ";

}

cout<<"\n\n";

cout <<"\tEnd of Program";

cout<<"\n\n";

}