For loops and addition - c++

Question

So I'm trying to use a for loop to fill the array with the numbers 1-8. Then add:
1 + 2 + 3 + 4 + 5 + 6 + 7 + 8 + numb = x
And then save it to an variable called x. I've done filling the array, but I don't know how to calculate the summary of the array + the number you enter. Would appreciate some help a lot.
#include <iostream>
using namespace std;
int main()
{
int array[8];
int numb;
int x; // x = summary of array + numb;
cin >> numb; // insert an number
for (int i = 0; i <= 8; i++)
{
array[i]=i+1;
}
for (int i = 0; i < 8; i++)
{
cout << array[i] << " + ";
}
}

Answer 1

Change the last part to:
x = numb;
for (int i = 0; i < 8; i++)
{
x = x + array[i];
}
cout<<x<<endl;
Realistically though, if you wanted to add the first n whole numbers, there's a formula:
(n*(n+1))/2;
so your whole program would be:
#include <iostream>
using namespace std;
int main()
{
int n = 8;
int numb;
cin >> numb; // insert an number
int x = n*(n+1)/2+numb;
cout<<x<<endl;
}

Answer 2

For the initial loop, remove the =:
for (int i=0; i<8; i++) { array[i]=i+1; }
For adding all the elements of an array, then adding numb:
var x=0;
for (int i=0; i<8; i++) { x += array[i]; }
x+=numb;
Then you can cout you x variable.

Answer 3

Unless you're required to use for loops and arrays (e.g., this is homework), you might want to consider code more like:
std::vector<int> array(8);
// fill array:
std::iota(begin(array), end(array), 1);
int numb;
std::cin >> numb;
int total = std::accumulate(begin(array), end(array), numb);
std::cout << "Result: " << total;