Consider the program:

#include <iostream>
using namespace std;

int main()
{

	int i, rows, j, k=1;

	cout<<"Enter the number of rows: ";
	cin>>rows;
	
	for(i=1; i<=rows; i++) {
		for(j=1; j<=i; j++) {
			cout<<k<<"\t";
			k++;
		}
		cout<<"\n";
	}

	return 0;
}

Explanation

We take the number of rows as the limit in the loop. The outer loop is for taking care of rows and the inner loop will take of the columns. Note that we have added the initializer j in the loop, as we need the value of k to increment for the next iterations as well. After the second loop we have printed a new line in order to show a new row.

This was the left oriented right angled puzzle. More puzzle like this coming soon.