Performing operations on a processed int vector
Never use using namespace std;. 
Some reasons why here
Part 1 is fine other than the error Bogdan Yarema pointed out. I would personally just start at 1 instead thought.

for (int i = 1; i &lt; intVector.size(); i++){

    int k = intVector[i] + intVector[i - 1];
    cout &lt;&lt; k &lt;&lt; endl;
}

In case the size of the vector is odd and the element in center should be added to himself (as Bogdan Yarema pointed out as swell), it would be better to get the ceiling of intVector.size() / 2

int half = (intVector.size() + 1 )/ 2;
int last = intVector.size() - 1;
for (int i = 0; i &lt; half; i++) {

    int k = intVector[i] + intVector[last - i];
    std::cout &lt;&lt; k &lt;&lt; std::endl;
}