PROB6_MAIN
  Demonstrate how a FORTRAN77
  program calls a C routine.

INT_ADD_SUB:
  Input I1 = 42.
  Input I2 = 22.
  Output I3 = 64.
 
  Set the value of two
  integers I1 and I2.
  Call a C routine to 
  compute I1 + I2.
 
  Input I1 =     42
  Input I2 =     22
  INT_ADD_SUB  returns I3 =     64
  INT_ADD_FUNC returns I4 =     64

REAL_ADD_SUB:
  Input R1 = 42.000000.
  Input R2 = 22.000000.
  Output R3 = 64.000000.
 
  Set the value of two reals R1 and R2.
  Call a C routine to compute R1 + R2.
 
  Input R1 =    42.0000    
  Input R2 =    22.0000    
  REAL_ADD_SUB  returns R3 =    64.0000    
  REAL_ADD_FUNC returns R4 =    64.0000    

DOUBLE_ADD_SUB:
  Input R1 = 42.000000.
  Input R2 = 22.000000.
  Output R3 = 64.000000.
 
  Set the value of two double precision 
  values D1 and D2.
  call a C routine to compute D1 + D2.
 
  Input D1 =    42.0000    
  Input D2 =    22.0000    
  DOUBLE_ADD_SUB  returns output D3 =    64.0000    
  DOUBLE_ADD_FUNC returns output D4 =    64.0000    
 
PROB6_MAIN:
  Normal end of execution.