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The Control Flow Loops

For Loop

The most commonly used loop - the for loop. This is extremely useful when you have to execute a given set of instruction a limited number of times with little or no changes.

Syntax:
for init test next body

I like this syntax better...
for { init } { test } { next } {
body
}


Now, for the first time we write a script to do something useful - make a multiplication table. Wondering how that is useful? You will find it very useful when you have forgotten mathematics - like me.

#Multiplication table...
set n 4 ;# We want the multiplication table of 4
set table ""
for { set i 1 } { $i <= 10 } { incr i } {
# This will append all multiples of all numbers for the number n 
#		into a variable called table
	set table "$table $i x $n = [expr $i \* $n]\n"
}

label .mul -text "Multiplication table for $n\n\n$table"
pack .mul

Foreach

Syntax:
foreach varName list body
This is a loop to make programming more easier. Primarily used for lists. Example...

#Make the list
set list [list "Item 1" {Item 2} Last]
set text ""
foreach item $list {
	#Append the every item to $text
	set text "$text\n$item"
}
#Shows the result
label .lab -text "$text"
pack .lab

The same can be achieved by a regular for loop like this.

#Make the list
set list [list "Item 1" {Item 2} Last]
set text ""
for { set i 0 } { $i <= [llength $list] } { incr i } {
	#Append the every item to $text
	set text "$text\n[lindex $list $i]"
}
label .lab -text "$text"
pack .lab