You can advance the value held in a variable, with:

count = count + 1

This is such a common operation that awk has a special operator for incrementing variables by 1.

++

The ++ operator increments the current value of the variable by 1. For example:

count++

adds 1 to the current value of count.

–␠–

The –␠– decrements (subtracts 1 from) the current value of a variable. For example, to subtract 1 from count, write:

count--