C  ================================================================================
C  =                                                                              =
C  =                    F O R T _ M A I N . F                                     =
C  =                                                                              =
C  ================================================================================
C 
C   Simple FORTRAN  Program driver program that uses the C Preprocessor
C
C
C   Note: To compile this program either use the makefile provided and type
C                     
C              make f_simple
C 
C         or simply enter the command: 
C                 
C                       f77 -e fort_main.F 
C
C         at the UNIX prompt.
C
C
C   ------------------------------------
C
C   NOTE: This program uses Pre-processor directives to define symbolic constants
C         and control conditional compilation. Use the -F option on f77 if you
C         want to view the pre-processed output that the compiler will see.
C


C
C Here we define some symbolic constants.
C Using the preprocessor, we've localized all the magic numbers in the program 
C so they're all defined at this point. Now if we want to change them, we only have
C to make a single change.
C
#define PI          3.14159265358979324    /* Universal Constant            */
#define OUTFILE    'out.dat'               /* Output filename               */
#define NPTS        30                     /* # Of data points to print     */
#define ILLUSTRATE_FUNCTION_CALL
#define ILLUSTRATE_SUBROUTINE_CALL

C
C  ================================================================================
C  =                       F _ S I M P L E                                        =
C  ================================================================================
C  Here is a simple main program. Use this as a skeleton for getting started with
C  your own FORTRAN programs.  
C 

      PROGRAM F_SIMPLE
      REAL    PARAM1
      INTEGER OUT_UNIT, I 


C  /*
C   * First we open a file and associate the filename given in the OUTFILE
C   * macro with the unit # 7. This gives you a basic output file to store
C   * your data. Use your FORTRAN reference to read about the 'STATUS' field
C   * and the implications of using the strings 'OLD' and 'NEW. 
C   */
      OUT_UNIT = 7
      open(UNIT=OUT_UNIT, FILE=OUTFILE, STATUS='OLD')

C  /*
C   * Next we write out some mindless text so you know the driver is running...
C   */
      write(6,*) ''
      write(6,*) ' -->   Hello World, This is the FORTRAN program driver...'
      write(6,*) ''

C
C    Here's an example illustrating a call to a subroutine. This section of 
C    code is enabled by setting the macro 'ILLUSTRATE_SUBROUTINE_CALL' with
C    either a #define or using the '-D' flag on the command line for the
C    compiler.
C
#ifdef ILLUSTRATE_SUBROUTINE_CALL
      PARAM1 = PI
      write(6,*)'Calling a fortran Subroutine'
      call fort_sub(PARAM1, OUT_UNIT)
      write(6,*)'Fortran Subroutine returned' 
      write(6,*) ''

#else
      write(6,*)''
      write(6,*)'Simple  Subroutine call not compiled.'
      write(6,*)'Define the macro: ILLUSTRATE_SUBROUTINE_CALL to compile in the call'  
      write(6,*)''
    
#endif



C
C     Here's and example illustrating the call to a function. THis section
C     of code is enabled by setting the macro 'ILLUSTRATE_FUNCTION_CALL' with
C     either a #define or using the -D flag to f77.
C
C
#ifdef ILLUSTRATE_FUNCTION_CALL

       write(6,*)'Calling a FORTRAN function'
       PARAM1 = fort_fcn( 6 )
       write(6,*)'Fortran Function returned: ',PARAM1
       write(6,*) ''

#else

      write(6,*)''
      write(6,*)'Simple Function call not compiled.'
      write(6,*)'Define the macro: ILLUSTRATE_FUNCTION_CALL to compile in the call'  
      write(6,*)''
#endif




C
C    Here's an example of some debugging code hidden behind the preprocessor
C    symbol DEBUG
C
#ifdef DEBUG
      write(6,*) ''
      write(6,*) ' This is a section of DEBUG Code... Print whatever you like here.'
      write(6,*) ''
#endif


C   /*
C    * Here's a loop to generate data from the Sine function
C    */
C
C

C
C    Here's the end of the program
C
      END