Variable Names

Here are two facts about variable names in C:

1. A variable name can contain letters (upper- and lower-case), digits, and underscores (the `_' character).
2. A variable name cannot start with a digit.

There are no restrictions on the length of C variable names. Let's look at some examples.

• X is an acceptable variable name.
• x_y is also acceptable.
• x+y is not acceptable, because it contains a plus sign.
• Epsilon is acceptable.
• TheFinalAnswer is acceptable.
• this_is_a_long_variable_name is acceptable.
• things_12 is acceptable.
• 12_things is not acceptable, because it starts with a digit.

Keep in mind that C is case-sensitive. For example, C treats the names Epsilon and epsilon as two different names.