All Operators (The GNU Awk User’s Guide)

From Get docs

6.2 Operators: Doing Something with Values

This section introduces the operators that make use of the values provided by constants and variables.

Arithmetic Ops    Arithmetic operations (‘+’, ‘-’, etc.)
Concatenation    Concatenating strings.
Assignment Ops    Changing the value of a variable or a field.
Increment Ops    Incrementing the numeric value of a variable.