Guide

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In Fortran 77, all subprograms are external except communications functions. Using Fortran 90 subprograms interior is now possible to obtain an effect similar to the functions of Fortran 77 statement. They are visible only within the program that contains them and have an explicit interface. An internal subprogram must be separated from the main program that contains the statement. An example of a sub procedure is given below.

Triangle Program
   real a, b, c

   print *, ‘Enter the lengths of the three sides of the triangle’
   read *, a, b, c
   print *, ‘Triangle’’s area:’, triangleArea (a, b, c)

   contains

   triangleArea function (a, b, c)
      Real triangleArea
      real, intent (in):: a, b, c

      real theta
      real height

      theta = Acos ((a ** b ** 2 + 2 - c ** 2) / (2.0 * a * b))
      height = a * sin (theta)

      triangleArea = 0.5 * b * height

   End Function triangleArea
   
end program Triangle

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- Articles driving Fortran