This is the GUI-version of [HiLo]:
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 # HiLo2.tcl - HaJo Gurt - 2005-06-20
 # Simple number-guessing-game with GUI

 #########.#########:#########^#########+#########-#########*#########$#####

  proc random { {range 100} } {
  # Return a number in the range 0 .. $range-1
    return [expr {int(rand()*$range)}]
  }

  proc Disp { {w .res1} {str ""} } {
  # Output string to one of the text-widgets
    $w insert end "\n"
    $w insert end $str
    $w see end          ;# scroll to bottom
  }

  proc Disable {} {
  # Disable entry-widget, highlight Newgame-Button
    .inp1 config -state readonly
    .but1 config -bg green
  }

  proc NewGame {} {
  # Start a new game
    set ::nGuess  0
   #set ::Secret 13
    set ::Secret [expr {[random $::Max] +1 }]

    .res1 delete 0.0 end
    .res2 delete 0.0 end
    Disp .res1 "  Guess my number:\n"
    Disp .res2 "   (1 .. $::Max)  \n"

    .inp1 config -state normal
    .but1 config -bg grey
  }

  proc TestNum {} {  ;# ??
  # Test if input is numeric
    set ok [string is integer $::Guess]
    if {$ok==0} {bell}
    return $ok
  }

  proc Update {} {
  # Process input, update display
    global Secret Guess nGuess

    set ok [string is integer $::Guess]
    if {$ok==0} {
      bell         ;# alert: input-error
    } else {
      incr ::nGuess
      if {$Guess <  $::Secret} { Disp .res1 "$Guess is too low"  }
      if {$Guess >  $::Secret} { Disp .res2 "$Guess is too high" }
      if {$Guess == $::Secret} { Disable
                                 Disp .res1 "$Guess is correct.\nYou needed $nGuess guesses.";
                               }
    }
    set Guess ""     ;# clear input-field
  }

  proc Init {} {
  # Initialize values, build GUI
    global Max Secret Guess nGuess
    set Max 100

    frame  .f1
    frame  .f2              ;# -bg blue -relief ridge
    pack   .f1 .f2 -pady 2

    text   .res1 -width 20 -height 10
    text   .res2 -width 20 -height 10
    pack   .res1 .res2  -in .f1  -side left

    tk_optionMenu .opt1 Max 16 64 100 128 256 512 1000 1024 2048 4096 8192
    button        .but1 -text "New game" -command {NewGame}
    label         .lx   -text ""         -anchor c -padx 12          ;# Spacer
    label         .lab1 -text "Guess:"
    entry         .inp1 -width 5         -textvariable Guess  ;#-validatecommand TestNum -validate key
    pack          .opt1 .but1 .lx .lab1 .inp1  -in .f2  -side left -padx 2 -pady 2

    bind          .inp1 <Return> {Update}

    wm title . "HiLo 2"
  }

  Init
  NewGame
  focus -force .inp1
----
[HJG] The options -relief and -validatecommand did not work as expected, 
but otherwise everything works fine.

[MG] The problem with your -validatecommand there is that you're checking the -textvariable for the widget, to see if the new text is valid. The way the validation works, though, is that you check before the value actually changes (and thus before the -textvariable is altered), to decide whether the change can happen or not. If you change it to use

  entry .inp1 -width 5 -textvariable Guess -validatecommand {TestNum %P} -validate key

then TestNum will be called with one arg - the %P will be substituted with the value of the entry widget if the change goes ahead. (There are several other validations available - check the 'Validation' section of the entry widget manpage.) In this particular instance, you'd want to check that the string entered is either a number, or blank - which your TestNum already does. So, all you need to do is change it to take an argument, and check that instead of $::Guess

  proc TestNum {value} {
  # Test if input is numeric
    set ok [string is integer $value]
    if {$ok==0} {bell}
    return $ok
  }

And then it should work OK. One other update you might want to add: In your Update proc, you use [[string is integer $::Guess]] to see if the update should go ahead. The problem with that is that the empty string passes the test. If you change that one to be [[string is integer -strict $::Guess]] it will stop people being able to guess "", and actually work on integers alone.

[MG] adds: the problem you're having with the -relief on the frame .f2 is that it's -borderwidth is set to 0. If you use 
 frame .f2 -bg blue -relief ridge -borderwidth 3
the ridge will show up. 
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[Category Games]