Advantages of Additions

The introduction of the previously mentioned new features have had an impact on the general standing of the language. Fortran 90 can be thought of as being: more natural, more flexible, more expressive, more usable, more portable and, above all, safer.

Even though FORTRAN 77 is a subset of Fortran 90 the user should steer away from `unsafe' features of the new language. Many `dangerous' features have been superseeded by new features of Fortran 90, for example,

• COMMON blocks -- use a module;
• EQUIVALENCE -- use TRANSFER; (using EQUIVALENCE also reduces portability);
• reshaping of arrays across procedure boundaries (this used to be possible when using assumed sized arrays) -- use the RESHAPE function at the call site;
• retyping of arrays across procedure boundaries -- use TRANSFER;
• reliance on labels has been decreased;
• fixed form source -- use free form;
• IMPLICIT NONE statement introduced which, if preset, disallows implicit typing of variables. (In FORTRAN 77 undeclared variables were implicitly declared with the type being derived from the first letter of the variable name -- this meant that wrongly spelled variable names could pass through a compiler with no warning messages issued at all. If the variable was referenced then a totally random value (the incumbent value of the memory location where the variable resides) would be used with potentially disastrous consequences.
• internal procedures (procedures within procedures with local scope) alleviate the need for the awkward ENTRY statements ans statement functions.

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