Learn Tcl - 10 Code Examples & CST Typing Practice Test

Tcl (Tool Command Language) is a lightweight, embeddable scripting language known for its simplicity, extensibility, and tight integration with the Tk GUI toolkit. It is widely used for rapid prototyping, automation, testing, GUI development, and embedded systems.

View all 10 Tcl code examples →

Tcl Counter and Theme Toggle Tcl Simple Addition Tcl Factorial Tcl Fibonacci Sequence Tcl Max of Two Numbers Tcl Array Sum Tcl Even Numbers Filter Tcl Conditional Counter Increment Tcl Resettable Counter Tcl Theme Toggle Only

Learn TCL with Real Code Examples

Updated Nov 20, 2025

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Code Sample Descriptions

Tcl Counter and Theme Toggle

set count 0
set isDark 0

proc updateUI {} {
    global count isDark
    puts "Counter: $count"
    puts "Theme: [expr {$isDark ? \"Dark\" : \"Light\"}]"
}

proc increment {} {
    global count
    incr count
    updateUI
}

proc decrement {} {
    global count
    incr count -1
    updateUI
}

proc reset {} {
    global count
    set count 0
    updateUI
}

proc toggleTheme {} {
    global isDark
    set isDark [expr {1 - $isDark}]
    updateUI
}

# Simulate actions
updateUI
increment
increment
toggleTheme
decrement
reset

Demonstrates a simple counter with theme toggling using Tcl variables and console output.

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Tcl Simple Addition

set a 10
set b 20
set sum [expr {$a + $b}]
puts "Sum: $sum"

Adds two numbers and prints the result.

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Tcl Factorial

set fact 1
for {set i 1} {$i <= 5} {incr i} {
    set fact [expr {$fact * $i}]
}
puts "Factorial: $fact"

Calculates factorial of 5 using a loop.

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Tcl Fibonacci Sequence

set fib0 0
set fib1 1
puts $fib0
puts $fib1
for {set i 3} {$i <= 10} {incr i} {
    set next [expr {$fib0 + $fib1}]
    puts $next
    set fib0 $fib1
    set fib1 $next
}

Generates first 10 Fibonacci numbers.

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Tcl Max of Two Numbers

set a 15
set b 25
if {$a > $b} {
    set max $a
} else {
    set max $b
}
puts "Max: $max"

Finds the maximum of two numbers.

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Tcl Array Sum

set nums {1 2 3 4 5}
set sum 0
foreach n $nums {
    set sum [expr {$sum + $n}]
}
puts "Sum: $sum"

Sums elements of an array.

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Tcl Even Numbers Filter

set nums {1 2 3 4 5}
foreach n $nums {
    if {[expr {$n % 2}] == 0} {
        puts "Even: $n"
    }
}

Prints even numbers from an array.

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Tcl Conditional Counter Increment

set count 3
if {$count < 5} {
    incr count
}
puts "Count: $count"

Increment counter only if less than 5.

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Tcl Resettable Counter

set count 0
incr count
incr count
incr count
puts "Count: $count"
set count 0
puts "Count after reset: $count"

Counter that increments and can be reset.

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Tcl Theme Toggle Only

set isDark 0
puts "Theme: [expr {$isDark ? \"Dark\" : \"Light\"}]"
set isDark [expr {1 - $isDark}]
puts "Theme: [expr {$isDark ? \"Dark\" : \"Light\"}]"
set isDark [expr {1 - $isDark}]
puts "Theme: [expr {$isDark ? \"Dark\" : \"Light\"}]"

Toggles theme multiple times.

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Frequently Asked Questions about Tcl

What is Tcl?

What are the primary use cases for Tcl?

Automation and scripting. GUI development with Tk. Network and telecom systems. Embedded systems command processors. Testing frameworks. EDA tool extensions & scripts

What are the strengths of Tcl?

Very easy to embed in apps. Excellent for GUIs via Tk. Strong ecosystem in testing/EDA. Minimalistic & quick to write. Great cross-platform support

What are the limitations of Tcl?

Performance slower than compiled languages. Less popular today for general-purpose coding. GUI (Tk) has an old-school native look. Syntax can feel unusual to newcomers. Limited modern library ecosystem compared to Python

How can I practice Tcl typing speed?

CodeSpeedTest offers 10+ real Tcl code examples for typing practice. You can measure your WPM, track accuracy, and improve your coding speed with guided exercises.

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Code Sample Descriptions

Tcl Counter and Theme Toggle

set count 0
set isDark 0

proc updateUI {} {
    global count isDark
    puts "Counter: $count"
    puts "Theme: [expr {$isDark ? \"Dark\" : \"Light\"}]"
}

proc increment {} {
    global count
    incr count
    updateUI
}

proc decrement {} {
    global count
    incr count -1
    updateUI
}

proc reset {} {
    global count
    set count 0
    updateUI
}

proc toggleTheme {} {
    global isDark
    set isDark [expr {1 - $isDark}]
    updateUI
}

# Simulate actions
updateUI
increment
increment
toggleTheme
decrement
reset

Demonstrates a simple counter with theme toggling using Tcl variables and console output.

Let’s Try →

Tcl Simple Addition

set a 10
set b 20
set sum [expr {$a + $b}]
puts "Sum: $sum"

Adds two numbers and prints the result.

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Tcl Factorial

set fact 1
for {set i 1} {$i <= 5} {incr i} {
    set fact [expr {$fact * $i}]
}
puts "Factorial: $fact"

Calculates factorial of 5 using a loop.

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Tcl Fibonacci Sequence

set fib0 0
set fib1 1
puts $fib0
puts $fib1
for {set i 3} {$i <= 10} {incr i} {
    set next [expr {$fib0 + $fib1}]
    puts $next
    set fib0 $fib1
    set fib1 $next
}

Generates first 10 Fibonacci numbers.

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Tcl Max of Two Numbers

set a 15
set b 25
if {$a > $b} {
    set max $a
} else {
    set max $b
}
puts "Max: $max"

Finds the maximum of two numbers.

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Tcl Array Sum

set nums {1 2 3 4 5}
set sum 0
foreach n $nums {
    set sum [expr {$sum + $n}]
}
puts "Sum: $sum"

Sums elements of an array.

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Tcl Even Numbers Filter

set nums {1 2 3 4 5}
foreach n $nums {
    if {[expr {$n % 2}] == 0} {
        puts "Even: $n"
    }
}

Prints even numbers from an array.

Let’s Try →

Tcl Conditional Counter Increment

set count 3
if {$count < 5} {
    incr count
}
puts "Count: $count"

Increment counter only if less than 5.

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Tcl Resettable Counter

set count 0
incr count
incr count
incr count
puts "Count: $count"
set count 0
puts "Count after reset: $count"

Counter that increments and can be reset.

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Tcl Theme Toggle Only

set isDark 0
puts "Theme: [expr {$isDark ? \"Dark\" : \"Light\"}]"
set isDark [expr {1 - $isDark}]
puts "Theme: [expr {$isDark ? \"Dark\" : \"Light\"}]"
set isDark [expr {1 - $isDark}]
puts "Theme: [expr {$isDark ? \"Dark\" : \"Light\"}]"

Toggles theme multiple times.

Let’s Try →

Frequently Asked Questions about Tcl

What is Tcl?

What are the primary use cases for Tcl?

Automation and scripting. GUI development with Tk. Network and telecom systems. Embedded systems command processors. Testing frameworks. EDA tool extensions & scripts

What are the strengths of Tcl?

Very easy to embed in apps. Excellent for GUIs via Tk. Strong ecosystem in testing/EDA. Minimalistic & quick to write. Great cross-platform support

What are the limitations of Tcl?

How can I practice Tcl typing speed?

CodeSpeedTest offers 10+ real Tcl code examples for typing practice. You can measure your WPM, track accuracy, and improve your coding speed with guided exercises.