**The program in C++ to display sum of series [ 9 + 99 + 999 + 9999 …] is given below:**

```
#include <iostream>
using namespace std;
int main() {
int n;
long long sum = 0;
cout << "Hello Codeauri Family,enter the number of terms in the series here: \n";
cin >>n;
for (int i = 1; i <= n; i++) {
int num = 0;
for (int j = 1; j <= i; j++) {
num = num * 10 + 9;
}
sum += num;
}
cout << "The sum of the series [9 + 99 + 999 + 9999 ...] for " << n << " terms is: " << sum << endl;
return 0;
}
```

## Output:

Hello Codeauri Family,enter the number of terms in the series here:

10

The sum of the series [9 + 99 + 999 + 9999 …] for 10 terms is: 2521176508

## Pro-Tips**💡**

This program prompts the user to enter an integer value for `n`

,

and then uses two nested for loops to generate the first `n`

terms of the series [ 9 + 99 + 999 + 9999 …] and calculate their sum.

The sum is then displayed at the end. Since the series sum is of order n^2, it’s a good practice to use long long variables.

Note that this program uses standard input/output library <iostream>

**Learn C-Sharp ↗**

C-sharp covers every topic to learn about C-Sharp thoroughly.

**Learn C Programming ↗**

C-Programming covers every topic to learn about C-Sharp thoroughly.

**Learn C++ Programming↗**

**Learn C++ Programming↗**

C++ covers every topic to learn about C-Sharp thoroughly.