Java program to check if a number is a duck number or not

Java program to check if a number is a duck number or not:

In this post, we will learn how to check if a number is a duck number or not in Java. We will write one program that will take a number as input from the user and print if it is a duck number or not.

What is a duck number:

A number is called a duck number if it contains at least one zero and if it is a positive number and it is not started with 0.

For example,

1234 is not a duck number because there is no zero in it.
12304 is a duck number because there is one zero.
01204 is not a duck number because it starts with a zero.
120034 is a duck number because it has two 0

Algorithm to check if a number is duck number or not:

We will use the below algorithm to check if a number is duck number or not:

Read the number as string and store it in a string variable
Check if the first character is zero or not. If yes, it is not a duck number.
If the first character is not zero, check all other characters one by one.
- If any of the characters is 0, it is a duck number.
- Else, it is not a duck number.

Method 1: Java program to check if a number is duck number or not:

Let’s write a Java program to check if a number is a duck number or not:

import java.util.Scanner;

public class Main {

    public static void main(String[] args) {
        String num;
        boolean isDuck;
        Scanner sc = new Scanner(System.in);

        System.out.println("Enter a number: ");
        num = sc.nextLine();

        if (num.charAt(0) == '0') {
            isDuck = false;
        } else {
            isDuck = false;
            for (int i = 1; i < num.length(); i++) {
                if (num.charAt(i) == '0') {
                    isDuck = true;
                    break;
                }
            }
        }

        if (isDuck) {
            System.out.println("It is a duck number");
        } else {
            System.out.println("It is not a duck number");
        }

    }
}

Here,

num is a string variable to hold the number. isDuck is a boolean value to define if the current number is duck or not.
It asks the user to enter a number, read it and store it in num.
If the first character is 0, it assigns false to isDuck.
If the first character is not 0,
- It assigns isDuck to false first and,
- By using a for loop, it iterates through other characters from index 1 to end.
- If it finds any character equal to 0, it marks isDuck to true and breaks from the loop.
At the end of the program, it checks the value of isDuck and prints one message based on it.

If you run this program, it will print output as like below:

Enter a number: 
01234
It is not a duck number

Enter a number: 
1234009890
It is a duck number

Enter a number: 
1234
It is not a duck number

Enter a number: 
012309
It is not a duck number

Method 2: Java program to check if a number is duck number or not by using a different method:

We can also use a different method to check if a number is a duck number or not. This method will take the number as the parameter and return one boolean value, true if it is a duck number and false if it is not.

Let me show you the full program:

import java.util.Scanner;

public class Main {

    public static boolean isDuck(String no) {
        if (no.charAt(0) == '0') {
            return false;
        }

        for (int i = 1; i < no.length(); i++) {
            if (no.charAt(i) == '0') {
                return true;
            }
        }

        return false;
    }

    public static void main(String[] args) {
        String num;
        Scanner sc = new Scanner(System.in);

        System.out.println("Enter a number: ");
        num = sc.nextLine();

        if (isDuck(num)) {
            System.out.println("It is a duck number");
        } else {
            System.out.println("It is not a duck number");
        }

    }
}

In this program,

isDuck is the method used to check if a number is a duck number or not.
- It takes one String as the input and returns one boolean value indicating the number is a duck or not.
The advantage of using a separate method is that we can call this method from any other file as well.
Inside this method,
- It first checks if the first character is 0 or not. If yes, it returns false, i.e. it is not a duck number.
- It iterates through the characters of the string starting from the second character. If it finds any character which is equal to 0, it returns true, i.e. it is a duck number.
- If the loop ends, i.e. if no character is 0 in that string, it returns false.

If you run this program, it will give similar output.

CodeVsColor

Java program to check if a number is a duck number or not