The Fortran language defines a number of names, or keywords, such as PRINT, INTEGER, MAX, etc. The spelling of these names is defined by the language. There are a number of entities that must be named by the programmer, such as variables, procedures, etc. These names must be chosen to obey a few simple rules. A name can consist of up to 31 alphanumeric characters (letters or digits) plus underscore. The first character in any name must be a letter. In names, upper and lower case letters are equivalent. The following are valid Fortran names,
A, aAa, INCOME, Num1, N12O5, under_score
The following declarations are incorrect statements due to invalid names,
INTEGER 1A ! does not begin with a letter INTEGER A_name_made_up_of_more_than_31_letters ! too long, 38 characters INTEGER Depth:0 ! contains an illegal character ":" INTEGER A-3 ! would be interpreted as subtract 3 from A
The underscore should be used to separate words in long names
user_name ! valid name
username ! different valid name
With this and the new long names facility in Fortran 90 symbolic names should be readable, significant and descriptive. It is worth spending a minute or so choosing a good name which other programmers will be able to understand.