57. Reversing flags
    ~~~~~~~~~~~~~~~
It is often necessary to use "flags" in a program. Eg.

 IF male%=TRUE THEN PRINT "Hello Sir" ELSE PRINT "Hello Madam"

where male% is a flag to indicate the sex of the user. If you need to
reverse the polarity of the flag, (ie change it from TRUE to FALSE and
vice-versa), you could use:

 IF flag%=TRUE THEN flag%=FALSE ELSE flag%=TRUE

However, this can be done much more simply, with:

 flag%=NOT(flag%)