**The program in C++ to Find Sum of Series 1 +11 + 111 + 1111 + .. n terms 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 + 1;
}
sum += num;
}
cout << "Well,the sum of the series [1 + 11 + 111 + 1111 + ..] for " << n << " terms is: " << sum << endl;
return 0;
}
```

## Output:

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

8

Well,the sum of the series [1 + 11 + 111 + 1111 + ..] for 8 terms is: 12345678

## 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 [ 1 + 11 + 111 + 1111 + ..] 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>

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