Updated 2011-05-12 02:14:40 by RLE

Purpose: To discuss the various looping constructs available in Tcl

One can do looping via

for start test next command
 for {set counter 1} {$counter <= 5} {incr counter} {
   puts $counter
 }

foreach varList list ?varList list ...? command
 foreach counter {1 2 3 4 5} {
   puts $counter
 }

 # varList example
 foreach {roman arabic} {
   I    1
   II   2
   III  3
   IV   4
   V    5
   VI   6
   VII  7
   VIII 8
   IX   9
   X    10
 } {
   puts "The roman numeral version of $arabic is $roman."
 }

 # multilist example
 foreach x {1 2 3 4 5} y {6 7 8 9 10} {
   puts "${x} x ${y} = [expr {$x*$y}]"
 }

while test command
 set counter 1
 while {$counter <= 5} {
   puts $counter
   incr counter
 }

or, if you have lots of breaking conditions, for example:
 set counter 1
 set start [ clock seconds ]
 while { 1 } {
   puts $counter
   if { [ incr counter ] >= 50000 } {
      break
   }
   if { [ expr {[ clock seconds ] - $start} ] >= 5 } {
      break
   }
 }