---- [http://mini.net/files/bits.jpg] if 0 { [Richard Suchenwirth] 2002-12-07 - Here is another educational Tcltoy: a set of 8 checkboxes that represent the bits of a byte. Each is labeled with its positional value below. The button at bottom displays the current value of the byte in hexadecimal, octal and decimal. Clicking on it resets all bits to 0, or, if they already are, to 1. The simple code below contains some tricks that are unique to Tcl. The positional values of the 8 bits serve as variable names as well, and with prefixed "." as widget names of the checkboxes. The two procedures first import the global list of positional values, then via [eval] [global] each of them separately. As name and ''onvalue'' of a "bit" are the same, the otherwise puzzling command set \$i \$i makes perfect sense - if i is 16, it assigns the value 16 to the variable 16... } set positionalValues {128 64 32 16 8 4 2 1} foreach i \$positionalValues { checkbutton .\$i -variable \$i -onvalue \$i -command compute lappend buttons .\$i lappend labels [label .l\$i -text \$i] } eval grid \$buttons eval grid \$labels button .result -textvar result -command reset -borderwidth 1 grid .result -columnspan 8 -sticky ew proc reset {} { global positionalValues result eval global \$positionalValues foreach i \$positionalValues { if {[lindex \$result end] == 0} { set \$i \$i } else {set \$i 0} } compute } proc compute {} { global positionalValues result eval global \$positionalValues set res 0 foreach i \$positionalValues { incr res [set \$i] } set result [format "Hex: 0x%02X, Octal: 0o%02o, Decimal: %d (%c)" \$res \$res \$res \$res] } compute ;# show the initial state (should be 0) bind . {exec wish \$argv0 &; exit} ---- 2002-12-09 JJM By changing these lines: grid .result -columnspan 8 -sticky ew set result [format "Hex: 0x%2X, Octal: 0o, Decimal: %d (%c)" \$res \$res \$res \$res] to these: grid .result -columnspan [llength \$positionalValues] -sticky ew set result [format "Hex: 0x%02X, Octal: 0o%02o, Decimal: %d" \$res \$res \$res] You can add an arbitrary number of values to the positionalValues list and the code will still work properly. It looks like this: [http://rohanpall.com/pub/coderx2-morebits.jpg] ----