HJG This is aimple demo of Tk: label, entry, button and an image.
A simple layout with frames and pack.
No shortcuts, e.g. combining statements and other tricks.
No error-checks on input (empty, non-numeric) or overflow of result.
#!/bin/sh
# Restart with tcl: -*- mode: tcl; tab-width: 4; -*- \
exec wish $0 ${1+"$@"}
# EntryDemo02.tcl - HaJo Gurt - 2006-02-02 - https://wiki.tcl-lang.org/15398
#: Tk-Demo: Enter 3 numbers, show their sum and product
package require Tk
proc Calc {} {
#: Calculate results / !! No error-checks !!
global A B C P S
#set S [ expr { $A + $B + $C } ]
#set P [ expr { $A * $B * $C } ]
# Force calculation as floating point:
set S [ expr { 0.0 + $A + $B + $C } ]
set P [ expr { double($A) * double($B) * double($C) } ]
}
#########1#########2#########3#########4#########5#########6#########7#####
frame .f1 ;# Frame for input-fields + button
frame .f2 ;# Frame for output
label .labA -text "A:"
label .labB -text "B:"
label .labC -text "C:"
label .labS -text "S="
label .labP -text "P="
entry .entA -textvar A -width 11
entry .entB -textvar B -width 11
entry .entC -textvar C -width 11
entry .entS -textvar S -state readonly
entry .entP -textvar P -state readonly
button .ok -text "OK" -command Calc
pack .f1 .f2
pack .labA .entA -in .f1 -side left
pack .labB .entB -in .f1 -side left
pack .labC .entC -in .f1 -side left
pack .ok -in .f1 -side left -padx 10
pack .labS .entS -in .f2 -side left
pack .labP .entP -in .f2 -side left
#package require Img ;# Images other than .gif
image create photo Pic1 -file "tcl.gif"
label .labPic1 -image Pic1
pack .labPic1 -padx 4 -pady 4
set A 2147483647 ;# MAXINT
set B 1
set C 2
Calc
bind . <Return> Calc
wm title . "EntryDemo2"
focus -force .entAIs there a simple/portable way to check for overflow, when working with integer values ?
expr problems with int, 32-bit integer overflow and Arbitrary Precision Math Procedures have some background, but I don't see a nice solution that fits into this program intended to be shown to beginners...
Lars H: The following, taken from Proper integers for Tcl 8.5 or 9.0, is probably the shortest way to check for addition overflow:
set sum_overflow [expr { $A+$B >> 1 != ($A>>1) + ($B>>1) + ($A&$B&1) }]For multiplication it is probably easiest to do the floating point operation and check the result magnitude, but if you feel a need to have a method completely robust against overflow then sum up the logarithms instead. Luckily this overflow problem will be gone in Tcl 8.5.
For pedagogical purposes, a better solution may be to pick something other than the product of three numbers as the function to demonstrate.
How about doing some date&time calculations, to let clock shine?
HJG: A demo with date&time calculations is a good idea, but surely a step up from working with 'simple numbers'.
I think it is better to cover the basics first.
links to pics have expired
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