Printing out sum of each pair of vector elements - C++ - c++

Question

I'm trying to printing out sum of each pair of adjacent elements in a vector. But the code shown below is not giving me the correct result. Anyone can help me with this?
int main()
{
vector <int> num(10);
vector <int> res(5);
int get = 0;
int range = 0;
for (int i = 0; i != 10; ++i) {
cin >> get;
num.push_back(get);
}
while (range != num.size()) {
int c = 0;
int c1 = c + 1;
res.push_back(num[c] + num[c1]);
if (c == 0)
c = 1;
c *= 2;
++range;
}
cout << res[7];
for (int u = 0; u != res.size(); ++u) {
cout << res[u] << " ";
}
return 0;
}
Update: -
I've changed this code as you mentioned in the comment section, but when I compile it showing me a debug error.
I able to read 1-10 integers into the 'num' vector. But when I hit enter after read all the integers into the vector, this debug error happens.
int main()
{
vector <int> num;
vector <int> res;
int get = 0;
int range = 0;
int c = 0, c1 = 0;
for (int i = 0; i != 10; ++i) {
cin >> get;
num.push_back(get);
}
while (range != num.size()) {
c1 = c + 1;
res.push_back(num[c] + num[c1]);
if (c == 0)
c = 1;
c *= 2;
++range;
}
for (int u = 0; u != res.size(); ++u) {
cout << res[u] << " ";
}
keep_window_open();
return 0;
}

Answer 1

Why are you doing this:
if (c == 0)
c = 1;
c *= 2;
What it does on first iteration is that c = 1 then it multiplies it by 2, so c=2 for 2nd iteration and c1 becomes 3.
So first your code will do num[0] + num[1] and in next iteration it will do num[2] + num[3] and third will do num[4] + num[5] and fourth will do num[8]+num[9] and so on.
I can see two approaches to this:
1) If you want to do adjacent addition like 0+1, 1+2, 2+3 then simply do c++ instead of those three lines of code.
2) If you want to do adjacent addition like 0+1, 2+3, 4+5 you can simply do c = c1+1 instead of those three lines of code.

Answer 2

I think the issue is in the loop increment.
Try this
while (range < num.size())
{
int c = 0;
int c1 = c + 1;
res.push_back(num[c] + num[c1]);
c += 2;
++range;
}

Answer 3

I had to change your code to make it compile and to make it reproducible (a good MCVE doesn't require user input):
#include <iostream>
#include <vector>
int main()
{
const std::vector<int> num =
{ 0, 0,
5, 10,
-5, 5,
3, -20};
std::vector<int> res;
unsigned int range = 0;
int c = 0, c1 = 0;
while (range != num.size()) {
c1 = c + 1;
res.push_back(num[c] + num[c1]);
if (c == 0)
c = 1;
c *= 2;
++range;
}
for (unsigned int u = 0; u != res.size(); ++u) {
std::cout << res[u] << " ";
}
}
Your problem is that you are multiplying c by two, instead of adding two, each iteration.
Here's a more idiomatic version:
#include <iostream>
#include <vector>
int main()
{
const std::vector<int> num
= { 0, 0,
5, 10,
-5, 5,
3, -20, };
std::vector<int> res;
const auto last = num.end();
for (auto it = num.begin(); it != last; ) {
auto v = *it++;
res.push_back(v + (it == last ? 0 : *it++));
}
for (auto v: res)
std::cout << v << " ";
std::cout << std::endl;
}
If this is homework, I suggest you make sure you understand it fully before you hand it in.

Answer 4

One solution using STL iterators:
#include <iostream>
#include <vector>
#include <numeric>
int main()
{
std::vector<int> v
{ 0, 0,
5, 10,
-5, 5,
3, -20};
for(auto& r : v) std::cout << r << "\t"; std::cout << std::endl; // print
//Calculate now the adjacent sum (sum of consecutive elements)
std::adjacent_difference(v.begin(), v.end(), v.begin(), [](const int x, const int y) { return x+y; });//here, set execution policy to parallel if wanted
v.erase(v.begin()); // pop_front
// print now every second element. Change i+=2 to i++ if you want every consecutive sum
for(size_t i = 0; i<v.size(); i+=2) std::cout << v[i] << "\t"; std::cout << std::endl;
return 0;
}
which results in:
0 0 5 10 -5 5 3 -20
0 15 0 -17

Answer 5

The biggest issue I see here, in addition to what was mentioned in the comments, is that you're only incrementing range by 1 instead of 2. This causes your code to overshoot the end of the vector, which means your sum is being corrupted by garbage data.