A Four Function Calculator

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Here's the calculator for when you just can't do it in your head:

Source:

Here is the source for the calculator:

# calc - A simple calculator for use as a plug-in demo.
# Sydney R. Polk, Sun Microsystems
#
# The global variable state is used to keep track of what the user has
# done. It has several fields: Whether or not the last button was a
# CE, the current value of the expression, the current value of the
# entry window.

proc doClear {} {
    global state

    set state(entry) "0."
    set state(dot) 0
    if {$state(entrystarted) == 0} {
	set state(result) "0."
	set state(operation) ""
    }
    set state(entrystarted) 0
}

proc doDot {} {
    global state

    set state(dot) 1
}

proc doAppend {what} {
    global state

    if {$state(entrystarted) == 0} {
	set state(entry) "0."
    }

    if {[string compare $state(operation) ""] == 0} {
	set state(result) "0."
    }

    if {!($what == 0 && [string compare $state(entry) "0."] == 0)} {
	set state(entrystarted) 1
        if {$state(dot) == 1} {
	    set state(entry) [format "%s%s" $state(entry) $what]
	} else {
	    regexp {([-0123456789]+).} $state(entry) foo integer

	    if {[string compare $integer "0"] == 0} {
		set state(entry) [format "%s." $what]
	    } else {
		set state(entry) [format "%s%s." $integer $what]
	    }
	}
    }    
}    

proc doOperation {what} {
    global state

    if {[string compare $state(operation) ""] != 0} {
	doEqual
    }
    set state(operation) $what
    set state(result) $state(entry)
    set state(entrystarted) 0
    set state(dot) 0
}

proc doEqual {} {
    global state

    if {[string compare $state(operation) ""] != 0} {
	set state(result) \
		[expr "$state(result) $state(operation) $state(entry)"]
    } else {
	set state(result) $state(entry)
    }
    set state(entry) $state(result)
    set state(entrystarted) 0
    set state(operation) ""
    set state(dot) 0
}

proc doSign {} {
    global state

    if {[string compare $state(entry) "0."] != 0} {
	set sign ""
	set abs ""
	regexp {([-]?)([0-9.]+)} $state(entry) foo sign abs
        if {[string compare $sign "-"] == 0} {
	    set state(entry) $abs
	} else {
	    set state(entry) [format "-%s" $abs]
	}
	set state(entrystarted) 1
    }
}

set state(result) "0."
set state(entry) "0."
set state(operation) ""
set state(dot) 0
set state(entrystarted) 0

label .label -textvariable state(entry) -justify right -anchor e

foreach {number} {0 1 2 3 4 5 6 7 8 9} {
    set buttons($number) [button .$number -text $number \
	    -command "doAppend $number"]
}
set buttons(clear) [button .clear -text C/CE -padx 1 -command "doClear"]
foreach {label operation} {div / mult * minus - plus +} {
    set buttons($label) [button .$label -text $operation \
	    -command "doOperation $operation"]
}
set buttons(dot) [button .dot -text . -command "doDot"]
set buttons(sign) [button .sign -text +/- -padx 1 -command "doSign"]
set buttons(equal) [button .equal -text = -command "doEqual"]

grid .label -column 0 -row 0 -columnspan 4 -sticky news
grid $buttons(clear) $buttons(div) $buttons(mult) $buttons(minus) -sticky news
grid $buttons(7) $buttons(8) $buttons(9) -sticky news
grid $buttons(4) $buttons(5) $buttons(6) -sticky news
grid $buttons(1) $buttons(2) $buttons(3) -sticky news
grid $buttons(0) $buttons(dot) $buttons(sign) -sticky news
grid $buttons(plus) -column 3 -row 2 -rowspan 2 -sticky news
grid $buttons(equal) -column 3 -row 4 -rowspan 2 -sticky news