Example: Octal to Decimal (Manual) in Java

// Octal to Decimal (Manual)
import java.util.Scanner;

// Main class containing the entry point of the program
public class Main {
    public static void main(String[] args) {
        Scanner scanner = new Scanner(System.in);

        // Step 1: Prompt user for an octal number
        System.out.print("Enter an octal number: ");
        int octalNumber = scanner.nextInt();

        // Step 2: Initialize decimal value and power
        int decimalNumber = 0;
        int power = 0; // Represents 8^0, 8^1, 8^2, etc.
        int tempOctalNumber = octalNumber; // Use a temporary variable for calculation

        // Step 3: Loop through each digit of the octal number
        while (tempOctalNumber != 0) {
            // Get the last digit of the octal number
            int digit = tempOctalNumber % 10;

            // Add the decimal equivalent of the digit to the total
            // digit * (8 ^ power)
            decimalNumber += digit * Math.pow(8, power);

            // Remove the last digit from the octal number
            tempOctalNumber /= 10;

            // Increment the power for the next digit
            power++;
        }

        // Step 4: Display the result
        System.out.println("Decimal equivalent: " + decimalNumber);

        scanner.close();
    }
}