@INC[string] returns
•1 if string is empty
•otherwise the same value as @EVAL[string + 1]
If string is the name of an environment variable, its value is used whether or not it is preceded by a percent mark % without modifying the value of the variable. To actually increment the value of the variable var use
set var=%@inc[%var]
Example:
set start=5
set result=%@inc[start]
echo %result
6