C++ Input handling

Question

How to take input for a scenario like this: first line contains the number of test cases, and subsequent lines are array elements without size.

Example input:

2
1 5 6 7 8
8 9 5 4 3

use a vector or follow this https://stackoverflow.com/questions/40437342/how-to-input-elements-in-an-array-without-inputting-n-c/40437475 — iwrestledthebeartwice, Aug 14 '21 at 07:33
Does this answer your question? [How to input elements in an array WITHOUT inputting n? (c++)](https://stackoverflow.com/questions/40437342/how-to-input-elements-in-an-array-without-inputting-n-c) — iwrestledthebeartwice, Aug 14 '21 at 07:34

score 0 · Answer 1 · answered Aug 14 '21 at 15:11

Here's an example, but it doesn't check for invalid input.

The key is to read each line using std::getline, then get it into an std::istreamstream. Then any method from this thread applies, if you replace std::cin with the name of your stringstream (ss in this example).

#include <iostream>
#include <iterator>
#include <limits>
#include <sstream>
#include <vector>

int main()
{
    // Read the number of lines.
    int n;
    std::cin >> n;

    // Skip the rest of the first line, including the line break.
    std::cin.ignore(std::numeric_limits<std::streamsize>::max(), '\n');

    // Repeat `n` times.
    while (n-- > 0)
    {
        // Read the next line.
        std::string line;
        std::getline(std::cin, line);

        // Construct a string stream from the line.
        // Now you can read from it as you would from `std::cin`.
        std::istringstream ss(line);

        // Get all numbers from the stream into an `std::vector`.
        std::vector<int> vec(std::istream_iterator<int>(ss), {});

        // Print the vector.
        for (int x : vec)
            std::cout << x << "; ";
        std::cout << '\n';
    }
}

I would use `while ((n-- > 0) && std::getline(std::cin, line)) { ... }` — Remy Lebeau, Aug 14 '21 at 17:16

C++ Input handling

1 Answers1