program prob2_main
!
!*******************************************************************************
!
!! PROB2_MAIN is a FORTRAN program that calls a C routine.
!
!
!  Routines in C are all called "functions", but if a C function is
!  "void", then it seems much like a FORTRAN subroutine.  Otherwise,
!  a C function is similar to a FORTRAN function.
!
  implicit none
!
  double precision d1
  double precision d2
  double precision d3
  double precision d4
  double precision double_add_func
  integer i1
  integer i2
  integer i3
  integer i4
  integer int_add_func
  real r1
  real r2
  real r3
  real r4
  real read_add_func
!
  write ( *, '(a)' ) ' '
  write ( *, '(a)' ) 'PROB2_MAIN'
  write ( *, '(a)' ) '  Demonstrate how a FORTRAN program '
  write ( *, '(a)' ) '  can call a C routine.'

  i1 = 42
  i2 = 22
  call int_add_sub ( i1, i2, i3 )
  i4 = int_add_func ( i1, i2 )

  write ( *, '(a)' ) ' '
  write ( *, '(a)' ) '  Set the value of two integers I1 and I2.'
  write ( *, '(a)' ) '  Call a C routine to compute I1 + I2.'
  write ( *, '(a)' ) ' '
  write ( *, '(a,i6)' ) '  I1 = ', i1
  write ( *, '(a,i6)' ) '  I2 = ', i2
  write ( *, '(a,i6)' ) '  C "subroutine" INT_ADD_SUB returns output I3 = ', i3
  write ( *, '(a,i6)' ) '  C function INT_ADD_FUNC returns output  I4 = ', i4

  r1 = 42.0E+00
  r2 = 22.0E+00
  call real_add_sub ( r1, r2, r3 )
  r4 = real_add_func ( r1, r2 )

  write ( *, '(a)' ) ' '
  write ( *, '(a)' ) '  Set the value of two reals R1 and R2.'
  write ( *, '(a)' ) '  Call a C routine to compute R1 + R2.'
  write ( *, '(a)' ) ' '
  write ( *, '(a,g14.6)' ) '  R1 = ', r1
  write ( *, '(a,g14.6)' ) '  R2 = ', r2
  write ( *, '(a,g14.6)' ) '  C "subroutine" REAL_ADD_SUB returns output R3 = ', r3
  write ( *, '(a,g14.6)' ) '  C function REAL_ADD_FUNC returns output  R4 = ', r4

  d1 = 42.0D+00
  d2 = 22.0D+00
  call double_add_sub ( d1, d2, d3 )
  d4 = double_add_func ( d1, d2 )

  write ( *, '(a)' ) ' '
  write ( *, '(a)' ) '  Set the value of two double precision values D1 and D2.'
  write ( *, '(a)' ) '  call a C routine to compute D1 + D2.'
  write ( *, '(a)' ) ' '
  write ( *, '(a,g14.6)' ) '  D1 = ', d1
  write ( *, '(a,g14.6)' ) '  D2 = ', d2
  write ( *, '(a,g14.6)' ) '  C "subroutine" DOUBLE_ADD_SUB returns output D3 = ', d3
  write ( *, '(a,g14.6)' ) '  C function DOUBLE_ADD_FUNC returns output  D4 = ', d4

  write ( *, '(a)' ) ' '
  write ( *, '(a)' ) 'PROB2_MAIN:'
  write ( *, '(a)' ) '  Normal end of execution.'

  stop
end