MAIN

  Demonstrate how a C main program
  may call a FORTRAN subroutine, and live!

  The C main program will now call the FORTRAN subroutine.

MAIN:
  Set integers I1 and I2, then call the FORTRAN subroutine 
  INT_ADD_SUB to compute I3 = I1 + I2.

  I1 = 42
  I2 = 22

  INT_ADD_SUB returned I3 = 64

  Now repeat, but using a FORTRAN function.

  INT_ADD_FUNC returned I3 = 64

MAIN:
  Set floats R1 and R2, then call the FORTRAN subroutine 
  REAL_ADD_SUB to compute R3 = R1 + R2.

  REAL_ADD_SUB returned R3 = 64.000000

  Now repeat, but using a FORTRAN function.

  REAL_ADD_FUNC returned R3 = 64.000000

MAIN:
  Set doubles D1 and D2, then call the FORTRAN subroutine 
  DOUBLE_ADD_SUB to compute D3 = D1 + D2.
 
  The FORTRAN routine INT_ADD_SUB received input:
    I1 =     42
    I2 =     22
  It is sending back the output:
    I3 =     64
 
  The FORTRAN routine REAL_ADD_SUB received input:
    R1 =    42.0000    
    R2 =    22.0000    
  It is sending back the output:
    R3 =    64.0000    
 
  The FORTRAN routine DOUBLE_ADD_SUB received input:
    R1 =    42.0000    
    R2 =    22.0000    
  It is sending back the output:
    R3 =    64.0000    

  DOUBLE_ADD_SUB returned D3 = 64.000000

  Now repeat, but using a FORTRAN function.

  REAL_ADD_FUNC returned R3 = 64.000000