Question

I’m trying to read multiple integers from a single input line into an array
eg. Input: 100 200 300 400, so the array is: a[0] = 100, a[1] = 200, a[2] = 300, a[3] = 400
The thing is, the number of integers are unknown, so the size of the array is unknown.

Answer 1

You should use a container that automatically resizes itself, such as std::vector.

For example, something like this:

#include <string>
#include <iostream>
#include <sstream>
#include <utility>
#include <iterator>

std::string line;
getline(instream, line);
std::istringstream this_line(line);
std::istream_iterator<int> begin(this_line), end;
std::vector<int> values(begin, end);