Java Program to Check Spy Number

A spy number is a number where the sum of its digits is equal to the product of its digits.

For example, 1124 is a spy number because 1+1+2+4 = 8 and 1×1×2×4 = 8.

1. Understanding the Problem

Determine whether a given number is a spy number.

Number: 1124 → Spy
Number: 123 → Not Spy
Number: 22 → Spy

2. Using Basic Loop

              
            
Java

          Check spy number using loop
        
import java.util.Scanner;

public class SpyNumber {
    public static void main(String[] args) {
        Scanner sc = new Scanner(System.in);
        System.out.print("Enter a number: ");
        int num = sc.nextInt();

        int sum = 0;
        int product = 1;

        while (num != 0) {
            int digit = num % 10;
            sum += digit;
            product *= digit;
            num /= 10;
        }

        if (sum == product)
            System.out.println("Spy Number");
        else
            System.out.println("Not a Spy Number");
    }
}

3. Optimized Approach

              
            
Java

          Check spy number using for loop
        
import java.util.Scanner;

public class SpyOptimized {
    public static void main(String[] args) {
        Scanner sc = new Scanner(System.in);
        System.out.print("Enter a number: ");
        int num = sc.nextInt();

        int sum = 0, product = 1;

        for (; num > 0; num /= 10) {
            int digit = num % 10;
            sum += digit;
            product *= digit;
        }

        if (sum == product)
            System.out.println("Spy Number");
        else
            System.out.println("Not a Spy Number");
    }
}

4. Common Mistakes

1. Initializing product as 0 instead of 1.

2. Forgetting to extract digits correctly.

3. Not handling single-digit numbers properly.

4. Mixing sum and product logic.

5. Applications

1. Helps in understanding digit-based operations.

2. Useful for practicing loops and arithmetic logic.

3. Common beginner-level coding problem.

Conclusion

Spy number programs are simple and useful for learning digit manipulation.

They help strengthen understanding of loops and basic arithmetic operations.