What is the effect of using prefix ++var versus postfix var++ in Bash arithmetic expansion?

• A. There is no difference.
• B. Prefix increments after; postfix before.
• C. Prefix increments before the value is used; postfix increments after.
• D. Prefix changes the type to string.

Answer: (C)

In Bash arithmetic expansion, the ++ operator has two forms with distinct timing for the value you get. The prefix form increments the variable first and then uses the new value in the expression. The postfix form uses the current value in the expression, then increments the variable after the value has been produced. This matches the behavior familiar from C-like languages.

For example, if you start with var=3:

• Using the prefix form in an expansion yields 4 and var becomes 4.

• Using the postfix form yields 3 in the expansion and then var becomes 4.

Be aware that if you reference the same variable multiple times in a single expression, the order Bash evaluates the parts can affect the result, so such expressions can be tricky.