🔢 Java Program to Count Number of Digits (With Explanation & Dry Run)

📌 Introduction

Counting the number of digits in a number is one of the basic Java number programs. This program is commonly asked in BCA exams, practicals, and interviews.
In this article, you will learn how to count the number of digits in Java using a simple loop.

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❓ What Does “Count Number of Digits” Mean?

It means finding how many digits are present in a given number.

Example

• Number: 12345

• Number of digits: 5

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🧠 Logic Used

• Each time we divide the number by 10, one digit is removed

• We increase the counter for every division

• Loop continues until the number becomes 0

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🧩 Algorithm to Count Number of Digits

1. Start

2. Read a number

3. Initialize count = 0

4. While number ≠ 0

   • count++

   • number = number / 10

5. Print count

6. End

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💻 Java Program to Count Number of Digits

import java.util.Scanner;

public class CountDigits {
    public static void main(String[] args) {
        int number, count = 0;

        Scanner sc = new Scanner(System.in);
        System.out.print("Enter a number: ");
        number = sc.nextInt();

        while (number != 0) {
            count++;
            number = number / 10;
        }

        System.out.println("Number of digits: " + count);
    }
}

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🧪 Dry Run

Input

number = 4567
count = 0

Step	number	count
1	4567	1
2	456	2
3	45	3
4	4	4

Final Output

Number of digits: 4

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🖥️ Output

Enter a number: 4567
Number of digits: 4

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📌 Special Case: Number = 0

👉 0 has 1 digit, but the loop will not run.

Solution for This Case

if (number == 0) {
    count = 1;
}

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🎯 Important Points for Exams

• / 10 removes one digit

• Loop runs once per digit

• Time Complexity: O(n)

• Works for all positive numbers