Question

So if i have a program that takes stdin such as

1
5
2
4

How exactly can i go through each line and say print that value, This is what im thinking:

#include <iostream>
using namespace std;

int main()
{

  while ( // input has ended// ) {
  cout << //current line//

  //increment to next line//

 }     

  return 0;
}

Is there such a way or no?

Answer 1

The pattern that I like is:

while (!cin.eof())
{
    string line;
    getline(cin, line);

    if (cin.fail())
    {
        //error
        break;
    }

    cout << line << endl;
}

As in the other answers, you can type CTRL+Z to send an EOF to STDIN. If STDIN is a pipe, then EOF will be sent when the stream has no more data.

To save into a vector:

vector<int> numbers;

while (!cin.eof())
{
    string line;
    getline(cin, line);

    if (cin.fail())
    {
        //error
        break;
    }

    cout << line << endl;

    istringstream iss(line);
    int num;
    iss >> num;
    numbers.push_back(num);
}

If you want a C-style array (although I would recommend std::vector:

size_t START_SIZE = 100;

size_t current_size = START_SIZE;
size_t current_index = 0;

int* numbers = new int[current_size];

while (!cin.eof())
{
    string line;
    getline(cin, line);

    if (cin.fail())
    {
        //error
        break;
    }

    cout << line << endl;

    if (current_index == current_size)
    {
        current_size += START_SIZE;
        int* tmp_arr = new int[current_size];

        for (size_t count = 0; count < current_index; count++)
        {
            tmp_arr[count] = numbers[count];
        }

        delete [] numbers;
        numbers = tmp_arr;
    }

    istringstream iss(line);
    int num;
    iss >> num;

    numbers[current_index] = num;
    current_index++;
}

delete [] numbers;