C++ Program:

Example:

    *
  * *
* * *
  * *
    *

#include <iostream>
using namespace std;

int main() {
  int columns,trows,k;
  cout<<"Enter number of columns: ";
  cin>>columns;
  trows=2*columns-1;
  k=trows;
  for(int i=trows; i>=1; i--) {
    for(int j=1; j<=trows; j++) {
      if(j<k)cout<<"  ";
      else cout<<"* ";
    }
    if(i<=columns)k++;
    else k--;
    cout<<endl;
  }
  return 0;
}

Output:

Enter number of columns: 4

      *
    * *
  * * *
* * * *
  * * *
    * *
      *

Main Logic :

trows=2*columns-1;   // trows : total rows to print
k=trows;  // Used to trigger decreasing order of *

for(int i=trows; i>=1; i--) {
   for(int j=1; j<=trows; j++) {
    if(j<k)cout<<"  ";
    else cout<<"* ";
  }
  //check for position change at which triangle * value to decrease
  if(i<=columns)k++;
  else k--;
  cout<<endl;
}

You can print any thing in this pattern, just replace your value with *