Example: Octal to Decimal Conversion in Java

// Octal to Decimal Conversion
import java.util.Scanner;

// Main class containing the entry point of the program
public class Main {
    public static void main(String[] args) {
        // Step 1: Create a Scanner object to read user input
        Scanner scanner = new Scanner(System.in);

        // Step 2: Prompt the user to enter an octal number
        System.out.print("Enter an octal number: ");
        String octalString = scanner.nextLine();

        // Step 3: Initialize variables for decimal equivalent and power of 8
        int decimal = 0;
        int power = 0;

        // Step 4: Iterate through the octal string from right to left
        for (int i = octalString.length() - 1; i >= 0; i--) {
            // Step 5: Get the current digit as a character
            char digitChar = octalString.charAt(i);

            // Step 6: Convert the character digit to an integer
            // Subtract '0' to get the integer value of the digit
            int digit = digitChar - '0';

            // Step 7: Check if the digit is valid for an octal number (0-7)
            if (digit < 0 || digit > 7) {
                System.out.println("Invalid octal number. Digits must be between 0 and 7.");
                scanner.close();
                return; // Exit the program if invalid
            }

            // Step 8: Calculate the decimal equivalent for the current digit
            // digit * (8 ^ power)
            decimal += digit * Math.pow(8, power);

            // Step 9: Increment the power for the next digit
            power++;
        }

        // Step 10: Print the resulting decimal number
        System.out.println("Decimal equivalent: " + decimal);

        // Step 11: Close the scanner to prevent resource leaks
        scanner.close();
    }
}