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FORTRAN 90+: IDENTIFIERS

A Fortran identifier is a variable or name. It MUST follow these rules:
  • The first character must be a letter (a-z).
  • It must be less than 32 characters (31 or less).
  • After the first character, the remaining characters can be letters (a-z), digits (0-9), or underscores (_).
  • Fortran does NOT differentiate between lower and upper case.
To go along with these rules, there are several good programming practices to follow:
  • Use upper case letters to identify Fortran keywords and intrinsic functions.
  • Use lower case letters to identify user-defined variables.
  • Use identifiers that are easy to follow (e.g., temp for temperature of a perfect gas), but that are not overly long (e.g., temperature_of_a_perfect_gas).
  • While one can use the same identifiers as Fortran keywords (e.g., sin and else) in some compilers, it is not good practice. Avoid using these.