Increment variable value by 1 (shell programming)

I can't seem to be able to increase the variable value by 1. I have looked at [tutorialspoint's *Unix / Linux Shell Programming* tutorial](http://www.tutorialspoint.com/unix/unix-basic-operators.htm) but it only shows how to add together two variables. I have tried the following methods but they don't work: i=0 $i=$i+1 # doesn't work: command not found echo "$i" $i='expr $i+1' # doesn't work: command not found echo "$i" $i++ # doesn't work*, command not found echo "$i" How do I increment the value of a variable by 1?