Syntax:
The /fpconstant option requests that a single-precision constant assigned to a double-precision variable be evaluated in double precision. If you omit /fpconstant (or specify the default /nofpconstant), a single-precision constant assigned to a double-precision variable is evaluated in single precision. The Fortran 90 standard requires that the constant be evaluated in single precision.
In the visual development environment, specify Extended Precision of Single-Precision Constants in the Floating Point (or Fortran Data) Compiler Option Category.
Certain programs created for FORTRAN-77 compilers (including Compaq Fortran 77) may show different floating-point results, because they rely on single-precision constants assigned to a double-precision variable to be evaluated in double precision.
In the following example, if you specify /fpconstant, identical values are assigned to D1 and D2. If you omit the /fpconstant option, the compiler will obey the standard and assign a less precise value to D1:
REAL (KIND=8) D1, D2
DATA D1 /2.71828182846182/ ! REAL (KIND=4) value expanded to double
DATA D2 /2.71828182846182D0/ ! Double value assigned to double