Scratch

A way to make it divide, subtract and multiply is to copy the script and replace the ()+() with ()*(), ()/() and ()-(). Then you can make it say something like
"Tell me a number."
"Now another"
"Would you like to Multiply, Divide, Subtract or Add?"
Then if they say Divide, it does the first number variable / by the second, etc.
If you don't understand much see http://scratch.mit.edu/projects/Death_Wish/1946019
It's a calculator I made 
And to make it have Square root you have to use the sqrt thing.