Description

To find sum of digits of a number, extract digits one by one and add them. For extraction find 
modulus, add it to previous modulus and divide number by 10 in a loop until number become 0.

C/C++

/* C Program to find sum of digits of a number */
//Save it as SumDigits.c

#include<stdio.h>
int main(){

    int number, sum=0, remainder;

    printf("Enter a number : ");
    scanf("%d",&number);

    while(number > 0){
        remainder = number % 10;
        sum += remainder;
        number /= 10;
    }

    printf("The sum of digits : %d", sum);

    return 0;
}

Input:
Enter a number : 
125

Output:
The sum of digits : 8

Java

/* Java Program to find sum of digits of a number */
//Save it as SumDigits.java

import java.io.*;
import java.util.Scanner;

public class SumDigits {

    public static void main(String[] args) {

            Scanner scanner = new Scanner(System.in);
        
            int number, sum=0, remainder;

        System.out.println("Enter a number : ");
        number = scanner.nextInt();

        while(number > 0){
            remainder = number % 10;
            sum += remainder;
            number /= 10;
        }

        System.out.println("The sum of digits : " + sum);
    }
}

Input:
Enter a number : 
125

Output:
The sum of digits : 8

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