C++ Exercises: Add up all the digits between two numbers

Last update on August 12 2025 12:50:01 (UTC/GMT +8 hours)

Sum of Digits Between Two Integers

Write a C++ program to add up all the digits between two given integers.
Add all the digits between 11 and 16.
// 11, 12, 13, 14, 15, 16
(1 + 1) + (1 +2) + (1 + 3) + (1 + 4) + (1 + 5) + (1 + 6)
= 2 + 3 + 4 + 5 + 6 + 7
= 27

Sample Data:

(5, 9) -> 35
(12, 18) -> 42
(39, 41) -> 21

Visual Presentation:

C++ Exercises: Add up all the digits between two numbers

Sample Solution-1:

C++ Code :

#include <iostream>

using namespace std;

// Function 'test' calculates the sum of digits for all numbers between x and y (inclusive)
int test(int x, int y)
{
    int digit_sum = 0;
    for(int i = x; i <= y; ++i)
    {
        int p = i;
        // Loop to extract digits and calculate their sum for each number between x and y
        while(p > 0)
        {
            digit_sum += p % 10; // Extract the last digit of the number and add it to digit_sum
            p /= 10; // Remove the last digit from the number
        }
    }
    return digit_sum; // Return the total sum of digits between x and y
}

int main() {
   // Define the range of numbers to calculate the sum of their digits
   int n1 = 39;
   int n2 = 41;

   // Display the range of numbers and the sum of their digits using the 'test' function
   cout << "Add up all the digits between " << n1 << " and " << n2 << " is: ";
   cout << test(n1, n2) << endl;
}

Sample Output:

Add up all the digits between 39 and 41 is: 21

Flowchart:

Sample Solution-2:

C++ Code :

#include <iostream>

using namespace std;

// Function 'test' calculates the sum of digits for all numbers between x and y (inclusive)
int test(int x, int y)
{
    int digit_sum = 0; // Initialize the variable to store the sum of digits
    int t = x; // Create a temporary variable to iterate from x to y
    while (t <= y) { // Loop through the numbers from x to y (inclusive)
        x = t; // Set x to the current value of t
        while (x) { // Loop to extract digits and calculate their sum for each number between x and y
            digit_sum += x % 10; // Extract the last digit of 'x' and add it to digit_sum
            x /= 10; // Remove the last digit from 'x'
        }
        ++t; // Move to the next number in the range
    }
    return digit_sum; // Return the total sum of digits between x and y
}

int main() {
   // Define the range of numbers to calculate the sum of their digits
   int n1 = 39;
   int n2 = 41;

   // Display the range of numbers and the sum of their digits using the 'test' function
   cout << "Add up all the digits between " << n1 << " and " << n2 << " is: ";
   cout << test(n1, n2) << endl;
}

Sample Output:

Add up all the digits between 39 and 41 is: 21

Flowchart:

For more Practice: Solve these Related Problems:

Write a C++ program to calculate the sum of all digits in the numbers between two given integers using loops and arithmetic operations.
Write a C++ program that adds the digits of each integer in a range and then outputs the total sum of all these digits.
Write a C++ program to compute the sum of digits of every number between two inputs, using a function to extract digits.
Write a C++ program that reads two integers, iterates through the range, sums the individual digits of each number, and prints the final total.

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