## A little primes toy

Richard Suchenwirth 2003-06-24: This educational Tcltoy (written on a PocketPC, but should run anywhere) shows the numbers from 1 to 100 on a canvas - see \$about for more. Maybe not a good starter to teach programming to children, but a nice visualitation of the Sieve of Erastothenes, and a factorization helper...

Richard Suchenwirth 2003

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.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

 Category Toys Arts and Crafts of Tcl-Tk Programming RS