Here you go,
class Program
{
static void Main(string[] args)
{
int n,i,j;
Console.Write("Enter size: ");
n = Convert.ToInt32(Console.ReadLine());
for (i = 1; i <= n; i++)
{
for (j = 1; j <= i; j++)
{
System.Console.Write("*");
}
System.Console.Write("\n");
}
Console.ReadLine();
}
}