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Like other programming language TCL also support decision making using control structure like if -else , switch. As you might know that everything is command in TCL, including if-else and switch.

if statement validate expression and if expression is true then, block of statement written under if statement is executed. Here is syntax of if else:

if {boolean_expression} { # This block will be executed if boolean expression is true }

One sample program based on above syntax:

set number 0

if { $number == 0 } {

puts "Number is zero"


Here if $number value is zero then expression will return true and as value of expression is true, statement written under if block will be executed.

Output :

C:\Tcl\bin>tclsh if_demo.tcl Number is zero

Lets check how can we use if-else statement. Syntax of if-else statement:

if { boolean_expression } { # If the boolean expression is true this block will get executed } else { # If the boolean expression is false this block will get executed }

Simple program based on if-else condition to check whether number is positive or negative.

set number 2

if { $number > 0 } {

puts "Number is Positive"

} else {

puts "Number is Negative"


Output is:

C:\Tcl\bin>tclsh if_else_demo.tcl Number is Positive