Help on bash script?

[Xu Qiang]

This is my test script: 

---------------------
#!/bin/bash

var=0
var=$[3]

vari=0
++vari

echo $var
echo $vari
---------------------

The result is: 
./test.sh: ++vari: command not found
3
0

So the manual of bash is incorrect? 

Regards,
Xu Qiang