#!/usr/bin/perl
# Tom Blum
# May 2007
# IWA-HWG Homework/ Instructor M. Kowalski

	print "\nThis program counts the number of simulated rolls \n";
	print "of two dice in order to get \"snake eyes\" (two ones)\n";
	print "or \"box cars\" (two sixes).\n\n";
	print "It performs this simulation over a number of trials and\n";
	print "determines the associated average and standard deviation.\n";  	

	print "\nEnter the number of trials you would like to run: ";
	chomp($sample_size = <STDIN>);
	if($sample_size < 1)
	{
		print "\nPlease enter the number of trials (e.g. 1000): ";
		chomp($sample_size = <STDIN>);
		if($sample_size < 1)
		{
			$sample_size = 1000;
			print "We will use a sample size of $sample_size.\n";
			
		}		
	}
	

	$sum_roll_count = 0;
	$sum_roll_count_squared = 0;
	for($i=0; $i<$sample_size; $i++)
	{	
		$die1=0;
		$die2=0;
		$roll_count = 0;
		until($die1+$die2==2 || $die1+$die2==12)
		{
			$roll_count++;
			$die1 = int(1 + rand 6);
			$die2 = int(1 + rand 6);
			#print "$roll_count: \t $die1,\t $die2\n";
		}
		#print "It required $roll_count rolls to roll snake eyes.\n";
		$sum_roll_count += $roll_count;
		$sum_roll_count_squared += $roll_count**2;
	}
	$roll_count_average = $sum_roll_count / $sample_size;
	$roll_count_squared_average =  $sum_roll_count_squared / $sample_size;
	$standard_deviation = sqrt($roll_count_squared_average-$roll_count_average**2);

	print "\nUsing a sample size of $sample_size, the following results were obtained.\n";
	print "The average number of rolls to roll snake eyes or box cars is $roll_count_average.\n";
 	print "The standard deviation is $standard_deviation.\n";