-U

Recognize upper and lower case in source files.

SPARC:77 x86:77

Do not treat uppercase letters as equivalent to lowercase. The default is to treat uppercase as lowercase except within character-string constants. With this option, the compiler treats Delta, DELTA, and delta as different symbols.

Portability and mixing Fortran with other languages may require use of -U. These are discussed in the Fortran Programming Guide. (Note that f90 does not have this option, always treating upper and lower case as equivalent.)