C++ Exercises: Display the sum of the specified series

Last update on April 07 2025 12:59:40 (UTC/GMT +8 hours)

23. Sum of the Series [9 + 99 + 999 + ...]

Write a program in C++ to display the sum of the series [ 9 + 99 + 999 + 9999 ...].

Visual Presentation:

C++ Exercises: Display the sum of the specified series

Sample Solution:-

C++ Code :

#include <iostream> // Including input-output stream header

using namespace std; // Using standard namespace to avoid writing std::

int main() // Start of the main function
{
    long int n, i, t = 9; // Declaration of long integer variables 'n' (number of terms), 'i' (loop counter), 't' (initial value of 9)
    int sum = 0; // Declaration of integer variable 'sum' initialized to 0 (to store the sum)

    cout << "\n\n Display the sum of the series [ 9 + 99 + 999 + 9999 ...]\n"; // Displaying a message on the console
    cout << "-------------------------------------------------------------\n";
    cout << " Input number of terms: "; // Prompting the user to input the number of terms
    cin >> n; // Reading the input value as the number of terms

    for (i = 1; i <= n; i++) // Loop to calculate 'n' terms of the series
    {
        sum += t; // Adding 't' (current term) to the sum
        cout << t << "  "; // Displaying the current term of the series
        t = t * 10 + 9; // Generating the next term of the series by multiplying 't' by 10 and adding 9
    }

    cout << "\n The sum of the series = " << sum << endl; // Displaying the sum of the series
}

Sample Output:

 Display the sum of the series [ 9 + 99 + 999 + 9999 ...]              
-------------------------------------------------------------          
 Input number of terms: 5                                              
9  99  999  9999  99999                                                
 The sum of the sarise = 111105

Flowchart:

For more Practice: Solve these Related Problems:

Write a C++ program to generate the series 9, 99, 999, ... for n terms and compute their sum.
Write a C++ program that constructs numbers of repeated 9's and adds them together, printing each term.
Write a C++ program to display a series where each term is formed by appending a 9 to the previous term, then output the total sum.
Write a C++ program that reads n and prints the series of numbers consisting of n repetitions of 9, followed by the sum of these numbers.

C++ Code Editor:

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