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Software Development in the UNIX Environment
Example Fortran 77 Program to Compute PI Using A Monte Carlo Method

Source code:

C Program to compute Pi using monte carlo methods

       program monte_pi
       implicit none
       integer niter,i,j
       integer seed 
       real*4 count
       real *8 x,y,pi(100),z
       real*8   rand
C initialize random numbers
       seed = 35791246
       call srand (seed)
       do j= 1,100
          niter = niter+100
          count =0
          do i=1,niter
             z= x*x +y*y
             if (z .le. 1) count =count+1
          end do
          pi(j)= count/niter*4.
          write(*,10) niter,pi(j)
10        format('Number of trials is: 'i5,'  estimate of pi is:',f8.5)
       end do

Command to compile and link : f77-o monte_pi monte_pi.f

Commands to compile and link in two steps:
1. f77 -c monte_pi.f - this produces object file monte-pi.o
2. f77 -o monte_pi monte_pi.o

Resulting executable: 32 -rwxr-xr-x 1 sas user 12580 Oct 11 14:25 monte_pi

Result of running monte_pi command:

Number of trials is: 100 estimate of pi is: 2.76000
Number of trials is: 200 estimate of pi is: 3.02000
Number of trials is: 300 estimate of pi is: 3.09333
Number of trials is: 9800 estimate of pi is: 3.12444
Number of trials is: 9900 estimate of pi is: 3.14424
Number of trials is: 10000 estimate of pi is: 3.12240

Command to run monte_pi and send output to a file:
monte_pi > monte.out