Write a Java program to calculate the sum of the digits of a given number

This program calculates the sum of the digits of a given number (userNo). Here’s a detailed breakdown of the logic:

What Does the Program Do?

Given an integer, the program extracts its digits, adds them together, and outputs the result.
For example:

• Input: 321
• Calculation: 3+2+1=6
• Output: Sum of digits: 6

class Main {
    public static void main(String[] args) {
        int userNo = 321;  // Input number
        int sum = 0;        // Variable to hold the sum of digits

        // Calculate the sum of the digits
        while (userNo != 0) {
            sum += userNo % 10;  // Add last digit to sum
            userNo /= 10;        // Remove last digit from the number
        }

        // Print the sum of digits
        System.out.print("Sum of digits: " + sum);
    }
}

Sum of digits: 6

Input Initialization:
userNo = 321: The number for which we calculate the sum of digits.
sum = 0: A variable to accumulate the sum of the digits.

Digit Extraction and Summation:

A while loop runs until userNo becomes 0.

Logic inside the loop:
userNo % 10: Extracts the last digit of userNo.
Example: For 321, 321 % 10 = 1 (last digit).
sum += userNo % 10: Adds the extracted digit to sum.
After the first iteration, sum = 0 + 1 = 1.
userNo /= 10: Removes the last digit from userNo by performing integer division by 10.
After the first iteration, userNo = 321 / 10 = 32.
Iteration Breakdown for userNo = 321:

Iteration 1:
Extract last digit: 1
Add to sum: sum = 0 + 1 = 1
Update number: userNo = 321 / 10 = 32
Iteration 2:
Extract last digit: 2
Add to sum: sum = 1 + 2 = 3
Update number: userNo = 32 / 10 = 3
Iteration 3:
Extract last digit: 3
Add to sum: sum = 3 + 3 = 6
Update number: userNo = 3 / 10 = 0
Loop ends when userNo becomes 0.

Output the Result:
After the loop, sum contains the total of all digits in the input number.
The program prints the result using System.out.print().