! 	  From: "COMPUTATIONAL PHYSICS, 2nd Ed" 
! 		by RH Landau, MJ Paez, and CC Bordeianu 
! 		Copyright Wiley - VCH, 2007.
! 		Electronic Materials copyright: R Landau, Oregon State Univ, 2007;
! 		MJ Paez, Univ Antioquia, 2007; and CC Bordeianu, Univ Bucharest, 2007.
! 		Supported by the US National Science Foundation				 
! 
! 	 pond.f90:  pi via Monte-Carlo integration (throwing stones)

Program pond

	Implicit none  
	Real*8 :: area, x, y, ranDom
	Integer :: i, max, pi
	
	max = 2000
                       ! open file, set initial value, seed generator
	Open(6, File = 'pond.dat', Status = 'Unknown')
	pi = 0
	                                                          ! execute
	Do i = 1, max       
	  x = ranDom()*2 - 1
		y = ranDom()*2 - 1 
		If ((x*x + y*y)  <= 1) then
		  pi = pi + 1
		Endif
		area = 4. * pi/Real(i)
		write(6, *) i, area
	End Do
	close(6)
	Stop 'data saved in pond.dat'
End Program pond