C++ Exercises: Add repeatedly all digits of a given non-negative number until the result has only one digit

Last update on April 12 2025 12:58:36 (UTC/GMT +8 hours)

11. Add Digits Until Single Digit (Digital Root)

Write a C++ program to add repeatedly all digits of a given non-negative number until the result has only one digit.

Input: 58
Output: 4
Explanation: The formula is like: 5 + 8 = 13, 1 + 3 = 4.

Sample Solution:

C++ Code :

#include <iostream>
using namespace std;

// Function to find the sum of digits of a number until a single digit is obtained
int addDigits(int num) {
    // Formula to get the sum of digits until a single digit is achieved
    return num - (num - 1) / 9 * 9;
}

int main(void) {
    // Test cases to find the single digit sum of numbers
    int n = 15;
    cout << "\nInitial number is " << n << " single digit number is " << addDigits(n) << endl;

    n = 57;
    cout << "\nInitial number is " << n << " single digit number is " << addDigits(n) << endl;

    return 0; // Return 0 to indicate successful completion
}

Sample Output:

Initial number is 15 single digit number is 6

Initial number is 57 single digit number is 3

Flowchart:

For more Practice: Solve these Related Problems:

• Write a C++ program to recursively sum the digits of a number until a single-digit result is obtained and print the digital root.
• Write a C++ program to calculate the digital root of a number using a loop and then compare the result with a mathematical formula.
• Write a C++ program that implements a recursive function to add the digits of an integer until a single digit remains, then output the number of iterations.
• Write a C++ program to read a number and repeatedly sum its digits until a one-digit number is produced, then display the process.

C++ Code Editor:

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