Incrementing number in bash

I have the following code and getting the error

./raytrac.bash: line 231: ((: 0++: syntax error: operand expected (error token is "+")
iarg = 0

       iarg=0
       narg=$#                   # Number of arguments passed.
       echo "narg = $narg"
       argsArr=("$@")            # Set array containing all arguments.
       while (($iarg < $narg))
       do
         echo "iarg = $iarg"
         arg=${argsArr[$iarg]}   # Bash arrays are zero-based: first element is indexed at 0.
         (($iarg++))
       done

((iarg++))