Basic Calculator with GUI
Tcl/Tk, 100

pack [entry .e -textv e] -f both -e 1
bind . &lt;Return&gt; {catch {expr $e} e}
bind . &lt;Escape&gt; {set e {}}


Buttons are not required, so leave them alone.
The GUI is great. So simple that you can finally focus on the task that you try to do.