# Draw a histogram on a canvas to display the
# following data values which are sales for the
# four quarters of a year

set info {103.7 154.6 206.5 178.7}

# Width and height of canvas, and border width

set wide 200
set tall 400
set border 50

# Procs to convert world to pixel co-ordinates

proc cvtx {x} {
   global xmult xadd
   return [expr 1.0 * $x / $xmult + $xadd]
   }

proc cvty {y} {
   global ymult yadd
   return [expr 1.0 * $y / $ymult + $yadd]
   }

# Work out the data range

set max 0
foreach number $info {
   if {$number > $max} {set max $number}
   }

# Work out conversion factors

set xmult [expr [llength $info] / (1.0 * $wide - 2 * $border)]
set ymult [expr $max / (-1.0 * ($tall - 2 * $border))]
set xadd $border
set yadd [expr $tall - $border]

set xr [expr $wide - $border]
set yb [expr $tall - $border]

canvas .histogram -width $wide -height $tall -background white
button .done -text done -command exit
pack .histogram .done -expand yes -fill both

.histogram create rect $border $border $xr $yb -outline black
for {set k 0} {$k < [llength $info]} {incr k} {
    set xlo [cvtx $k]
    set xhi [cvtx [expr $k + 1]]
    set ylo [cvty 0]
    set yhi [cvty [lindex $info $k]]
    .histogram create rect $xlo $ylo $xhi $yhi -outline black -fill yellow
    }