23.3: Example

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A simple example program to generate 100 random integer numbers, each between 1 and 100, is as follows:

program rand

implicit none
integer, parameter :: rcount=100
integer :: i
integer, dimension(rcount) :: nums
real :: x

    call random_seed()

    do i = 1, rcount
        call random_number(x)
        nums(i) = int(x*100.0) + 1
    end do

    write (*,'(a)') "Random Numbers:"
    do i = 1, rcount
        write (*,'(i3,2x)', advance="no") nums(i)
        if (mod(i,10)==0) write (*,*)
    end do

end program rand

The call to random_seed() must be performed before the call to random_number(). Additionally, the call to random_seed() can only be performed once.

The output of this example program is shown below:

Random Numbers:
100  57  97  75  37  49   8   1  35  35
 22  14  91  39  45  67   2  66  65  33
 86  41  21  97  60  68  46  34  11  76
 61  72  90  66  16  62  98 100  26  56
 66  56  98  91  66  73  41  93  15  68
 77  34  12  62  83  95  74  50  38  43
 56 100 100  75  96  10  74  76  95  71
 82  56   7  49  60  14  59  52  89  31
 67  67  51  27   8  11  55  38   2  80
 63  78  96  12  32  60   5  12  22  11

Each execution will generate the same series of random numbers.