Rules of naming variables

• Names are made up of LETTERS or DIGITS or _
• First character must be LETTER
  • Can also begin with _
  • However, don't begin variable names with _ since library routines often use such names.
• UPPER and lower letters are distinct.
  • Meaning hello is different from HELLO

• Traditional Practice is to use UPPER for symbolic constants, lower for variables
• We tend to use
  • short names for local variables (especially loops)
  • longer names for external variables

At least the first 31 characters of an internal name are significant.
For function names and external variables, the number may be less than 31,
because external names may be used by assemblers and loaders over which the language has no control.
For external names, the standard guarantees uniqueness only for 6 characters and a single case. Keywords like if, else, int, float, etc., are reserved: you can't use them as variable names.