#include<iostream>
using namespace std;

int main()
{
int i,j,n;
cout<<"Enter the No Of Row\n";
cin>>n;
char c='A';
   for(i=0;i<n;i++)
   {
   for(j=0;j<=i;j++)
   {
   if(c=='Z')
   break;
  cout<<c;
  c++;
   }
  cout<<"\n";
  }
  return 0;
}

Output:

Enter the No of Row

6

A

BC

DEF

GHIJ

KLMNO

PQRSTU