Multi-line stdin - C++

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;

Answer 2

The simplest way is to do it like this (similar was suggested but the .fail() and .eof() functions of std::istream shouldn't usually be used like that):

int main (int argc, char* argv[])
{
   std::string line;
   while (std::getline (std::cin, line))
   {
     std::cout << line << std::endl; // std::getline skips the newline
   }

   std::cout << "No more lines" << std::endl;
   return 0;
};

Answer 3

You can add an ending condition like 0 if you are reading from console. If user enters 0 it will end taking input.

#include <iostream>
using namespace std;

int main()
{
  int n;
  cin>>n;
  while(n!=0) {

  cout << //current line//

  //increment to next line//
  cin>>n;
 }   

  return 0;
}

Answer 4

How about std::cin >> std::cout.rdbuf(); ? It will end when you enter EOF via CTRL-Z or likewise. Here's a sample :

#include <iostream>

int main() {
    std::cin >> std::cout.rdbuf();
}

Input:

1
5
4
2
(EOF)

Output:

1
5
4
2

Saving them into an array and printing them later works just as well:

std::vector<int> inputs(std::istream_iterator<int>(std::cin), std::istream_iterator<int>());
std::copy(std::begin(inputs), std::end(inputs), std::ostream_iterator<int>(std::cout, "\n"));