Kotlin program: Calculate the factorial of a given number

Last update on February 04 2025 06:50:14 (UTC/GMT +8 hours)

Write a Kotlin program to find the factorial of a given number.

Pre-Knowledge (Before you start!)

• Basic Kotlin Syntax.
• Kotlin Functions.
• Variables and Data Types.
• Conditional Statements.
• Loops.
• Factorial Concept.
• String Interpolation.

Hints (Try before looking at the solution!)

• Define the main() Function.
• Create a Factorial Function.
• Use a Loop.
• Return the Result.
• Call the Function.
• Display the Output.
• Test with Different Numbers.
• Common Errors to Avoid:
  • Forgetting edge cases like 0 or 1.
  • Using Int instead of Long for large results.
  • Misplacing logic in if-else or loops.

Sample Solution:

Kotlin Code:

fun main() {
    val number = 5
    val factorial = calculateFactorial(number)
    println("Factorial of $number: $factorial")
 }

fun calculateFactorial(number: Int): Long {
    return if (number == 0 || number == 1) {
        1
    } else {
        var result = 1L
        for (i in 2..number) {
            result *= i
        }
        result
    }
}

Sample Output:

Factorial of 5: 120

Explanation:

In the above exercise,

• Inside the "main()" function, a variable named 'number' is declared and assigned a value of 5.
• The calculateFactorial() function is then called with the number as an argument, and the result is stored in a variable named factorial.
• Finally, the result is printed using string interpolation in the println() statement: "Factorial of $number: $factorial".

In the calculateFactorial() function,

• The function takes an integer number as a parameter and returns the factorial as a Long value.
• Inside the function, an if statement checks if the number is equal to 0 or 1. If it is, the function returns 1 because the factorial of 0 and 1 is 1.
• If the number is greater than 1, the function initializes a variable result with 1L, indicating the starting value for the factorial calculation.
• A for loop is used, starting from 2 (as the factorial calculation starts from 2) and continuing until number. In each iteration, the result is multiplied by i and assigned back to the result.
• Finally, the calculated factorial is returned.

Kotlin Editor:

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