C++ Code to Print * To Get A Christmas Tree

C++  Code to Print * To   Get a Christmas Tree

===================================

#include <iostream>
using namespace std;
int main()
{

    cout<<"***********CHRISTMAS TREE**************\n\n";
    int a,b;
    string c,d;
    cout<<"Enter the number of rows: ";
    cin>>a;

    for(b=1; b<=a; b++)
    {
  for(int x=a-1; x>=b; x--)
        {
            cout<<" ";
        }

for(int x=1; x<=b; x++)
        {
            cout<<"* ";
        }
        cout<<endl;

    }
}