set about "primes.tcl

Richard Suchenwirth 2003
Powered by Tcl/Tk!

Click on a number to highlight its multiples, and see its prime factors on top.
Click Clear to remove highlighting.
Primes are never highlighted. They are multiples only of 1, which is no prime.
(Hint: 2 3 5 7)"

# to make it work with tclkit...
package require Tk

proc main {} {
    frame .f
    label .f.l -width 26 -bg white -textvar info
    button .f.a -text About  -command {tk_messageBox -message $about}
    button .f.c -text Clear -command {.c itemconfig txt -fill black}
    button .f.x -text X -command exit
    eval pack [winfo children .f] -side left -fill y
    pack .f [canvas .c]
    set x 20; set y 20
    set n 0
    foreach row {1 2 3 4 5 6 7 8 9 10} {
        foreach col {1 2 3 4 5 6 7 8 9 10} {
            .c create text $x $y -text [incr n] -tag txt
            incr x 20
        }
        set x 20; incr y 20
    }
    .c bind txt <1> {hilite .c}
    wm geometry . 240x268+0+0
}

proc hilite w {
    set id [$w find withtag current]
    set ::info $id=[join [primefactors $id] *]
    if {$id == 1} return
    for {set i [expr $id+1]} {$i<=100} {incr i} {
        if {$i%$id == 0} {
            $w itemconfig $i -fill orange
        }
    }
}
proc primefactors n {
    set res {}
    for {set i 2} {$i <= $n} {incr i} {
        while {$n%$i == 0} {
            set n [expr {$n/$i}]
            lappend res $i
        }
    }
    set res
}
main