Learn K with Real Code Examples

Updated Nov 20, 2025

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Code Sample Descriptions

K Counter and Theme Toggle

count:0
isDark:0

updateUI:{
    'Counter: ', string count
    'Theme: ', (if[isDark; 'Dark'; 'Light'])
}

increment:{
    count+:1
    updateUI[]
}

decrement:{
    count-:1
    updateUI[]
}

reset:{
    count:0
    updateUI[]
}

toggleTheme:{
    isDark:1-isDark
    updateUI[]
}

/ Simulate actions
updateUI[]
increment[]
increment[]
toggleTheme[]
decrement[]
reset[]

Demonstrates a simple counter with theme toggling using K variables and functional style.

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K Fibonacci Sequence

fib:0 1
10{fib,:{x,y:x+y} last 2 fib}

Generates first 10 Fibonacci numbers using K arrays.

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K Factorial Calculator

fact:{[n] $[n=0;1;n*fact[n-1]]}
fact[5]

Calculates factorial of a number using K's functional style.

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K Prime Checker

isPrime:{[n] n>1 & all n mod 2_til n-1}
isPrime[13]

Checks if a number is prime using modulo and all.

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K Sum of Array

+/ 1 2 3 4 5

Calculates the sum of an array.

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K Reverse String

'HELLO' _/

Reverses a string.

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K Multiplication Table

{x*til 10}[5]

Generates multiplication table for a number.

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K Celsius to Fahrenheit

{x*9%5+32}[25]

Converts Celsius to Fahrenheit.

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K Simple Alarm Simulation

temp:80
thresh:75
$[temp>thresh;'Alarm: Temp Too High!';'Temp Normal']

Simulates an alarm if threshold exceeded.

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K Random Walk Simulation

steps:10
pos:0
10{pos+:2?2-1; pos}

Simulates a 1D random walk.

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Code Sample Descriptions

K Counter and Theme Toggle

count:0
isDark:0

updateUI:{
    'Counter: ', string count
    'Theme: ', (if[isDark; 'Dark'; 'Light'])
}

increment:{
    count+:1
    updateUI[]
}

decrement:{
    count-:1
    updateUI[]
}

reset:{
    count:0
    updateUI[]
}

toggleTheme:{
    isDark:1-isDark
    updateUI[]
}

/ Simulate actions
updateUI[]
increment[]
increment[]
toggleTheme[]
decrement[]
reset[]

Demonstrates a simple counter with theme toggling using K variables and functional style.

Let’s Try →

K Fibonacci Sequence

fib:0 1
10{fib,:{x,y:x+y} last 2 fib}

Generates first 10 Fibonacci numbers using K arrays.

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K Factorial Calculator

fact:{[n] $[n=0;1;n*fact[n-1]]}
fact[5]

Calculates factorial of a number using K's functional style.

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K Prime Checker

isPrime:{[n] n>1 & all n mod 2_til n-1}
isPrime[13]

Checks if a number is prime using modulo and all.

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K Sum of Array

+/ 1 2 3 4 5

Calculates the sum of an array.

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K Reverse String

'HELLO' _/

Reverses a string.

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K Multiplication Table

{x*til 10}[5]

Generates multiplication table for a number.

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K Celsius to Fahrenheit

{x*9%5+32}[25]

Converts Celsius to Fahrenheit.

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K Simple Alarm Simulation

temp:80
thresh:75
$[temp>thresh;'Alarm: Temp Too High!';'Temp Normal']

Simulates an alarm if threshold exceeded.

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K Random Walk Simulation

steps:10
pos:0
10{pos+:2?2-1; pos}

Simulates a 1D random walk.

Let’s Try →