If Else statement in TCL

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