Step by Step solution about How to resolve the algorithm Luhn test of credit card numbers step by step in the Kotlin programming language

Explanation:

1. Overview:

This Kotlin program checks the validity of credit card numbers using the Luhn algorithm, which is a checksum formula used to detect errors in numerical data.

2. Function:

• checkLuhn(number: String): Boolean

Function Arguments:

• number: The credit card number as a string to be checked.

Function Logic:

• isOdd: A boolean flag used to alternate the calculations for each digit in the credit card number.
• sum: An integer to keep track of the total sum of the calculated digits.

The function iterates through the digits of the credit card number from right to left (reversed order). For each digit:

• It converts the character to an integer by subtracting the ASCII value of '0' (number[index] - '0').
• If isOdd is true, it adds the digit to the sum.
• If isOdd is false, it doubles the digit, calculates the sum of its two digits, and adds it to the sum.
• It alternates isOdd to apply the correct calculation (doubling or not) for the next digit.

After iterating through all digits, the function checks if sum % 10 is equal to 0. If it is, the credit card number is considered valid according to the Luhn algorithm. Otherwise, it's considered invalid.

3. Main Function:

• main(args: Array<String>)

Main Function Logic:

The main function is the entry point of the program. It contains an array of credit card numbers (numbers) to be checked.

• It iterates through each credit card number in the array.
• For each number, it calls the checkLuhn function and prints the result ("valid" or "invalid") along with the number.

4. Output:

The program outputs the following:

49927398716      is valid
49927398717      is invalid
1234567812345678 is valid
1234567812345670 is invalid

In this example, the first and third credit card numbers are valid, while the second and fourth are invalid.

// version 1.0

fun checkLuhn(number: String): Boolean {
    var isOdd = true
    var sum = 0

    for (index in number.indices.reversed()) {
        val digit = number[index] - '0'
        sum += if (isOdd) digit else (digit * 2).let { (it / 10) + (it % 10) }
        isOdd = !isOdd
    }

    return (sum % 10) == 0
}

fun main(args: Array<String>) {
    val numbers = arrayOf("49927398716", "49927398717", "1234567812345678", "1234567812345670")
    for (number in numbers)
        println("${number.padEnd(16)} is ${if(checkLuhn(number)) "valid" else "invalid"}")
}