Reading an unknown number of inputs

Question

I need to read an unknown number of inputs using either C++ or Java. Inputs have exactly two numbers per line. I'd need to use cin or a System.in Scanner because input comes from the console, not from a file.

Example input:

1 2

3 4

7 8

100 200

121 10

I want to store the values in a vector. I have no idea how many pairs of numbers I have. How do I design a while loop to read the numbers so I can put them into a vector?

Answer 1

You can use an idiomatic std::copy in C++: (see it work here with virtualized input strings)

std::vector<int> vec;
std::copy (
    std::istream_iterator<int>(std::cin), 
    std::istream_iterator<int>(), 
    std::back_inserter(vec)
);

That way, it will append onto the vector each time an integer is read from the input stream until it fails reading, whether from bad input or EOF.