14.1.1 Language Extensions

g77 offers several extensions to FORTRAN 77 language that f2c doesn't:

• Automatic arrays
• CYCLE and EXIT
• Construct names
• SELECT CASE
• KIND= and LEN= notation
• Semicolon as statement separator
• Constant expressions in FORMAT statements (such as `FORMAT(I<J>)', where `J' is a PARAMETER named constant)
• MvBits intrinsic
• libU77 (Unix-compatibility) library, with routines known to compiler as intrinsics (so they work even when compiler options are used to change the interfaces used by Fortran routines)

g77 also implements iterative DO loops so that they work even in the presence of certain “extreme” inputs, unlike f2c. See Loops.

However, f2c offers a few that g77 doesn't, such as:

• Intrinsics in PARAMETER statements
• Array bounds expressions (such as `REAL M(N(2))')
• AUTOMATIC statement

It is expected that g77 will offer some or all of these missing features at some time in the future.