How can I get a return value from a Tk script?

[nashuakid]

I run the following script from a C-program under Mac OS (Snow Leopard) with the system () command:

#!/usr/local/bin/wish
set answer [tk_messageBox -message "Really quit?" -type yesno -icon question]
switch -- $answer {
yes exit 1
no exit 2
}

When returning from the script the C program needs to know what button was clicked.
Can someone help?

Thank you.