How to read multiple lines from user in C++?

Question

So I'm doing acm programming practice problems and I'm always stuck on getting input from user. I'm using C++. So I need to read input from user and it could be multiple lines or a single line we don't know. So if the input is as follow:

2

1 2 3 4 5

2 2 2

The first line represent the number of games that the user play and the lines follow are the scores. The end of each game will be terminated by a newline. I need to read those lines and store it somewhere. How do I go about doing that? I've looked on websites and it seems like most people use scanf or cin or getline but I have no clue what those does.

Another example:

12 21

13 43

1 4

A C

0 0

Each line will contain the two number I need to add, separated by whitespace. When I see two zeros, the input is done. How do I read these and check if it's 0 0? I tried something like:

string num1;
while (true) {
    getline(cin,num1);
    if (num1.empty()) {
        break;
    }
}

But it didn't work. Please help I think I know how to solve the problem but I can't the point of getting input from user. Thanks

What you tried "didn't work"? How did it "not work"? Did you get any error messages? What the value not what you expected? — Chad, Feb 05 '14 at 16:09
'most people use scanf or cin or getline but I have no clue what those does' - try googling for them? http://www.cplusplus.com/reference/cstdio/scanf/ http://www.cplusplus.com/reference/iostream/cin/ http://www.cplusplus.com/reference/string/string/getline/ — Graeme, Feb 05 '14 at 16:14
You should consider getting a decent [book](http://stackoverflow.com/questions/388242/the-definitive-c-book-guide-and-list). — molbdnilo, Feb 05 '14 at 16:18
Well the input ends with newline. For the code above I have to have two newlines to end the input. — user2649966, Feb 05 '14 at 18:33
I you want the _idea_ here you are: if every input of the same structure - create such `structure` or `class`, define `operator>>` (for input) and/or `operator<<` (for output). Also take a look at `stringstream` and as you've already figured out `getline`. Here is [reference](http://en.cppreference.com/) — Yuriy Ivaskevych, Jan 24 '17 at 14:58

score 0 · Answer 1 · answered Feb 05 '14 at 17:11

Well, I learned this from doing online challenges and this is the way I do this when necessary.

First case, I think you have to declare N cases, so I have:

int N;

Then, we need multiple numbers in each case, let's say 3. So I'll do this:

int score1[N];
int score2[N];
int score3[N];

Finally, when you have to take input, you do this:

cin >> N;

for(int i = 0; i < N; i++)
    cin >> score1[i] >> score2[i] >> score3[i];

I'm not sure if this is the best way to do this, but this is how I do it when I am doing online challenges. Good luck!

score 0 · Answer 2 · answered Feb 05 '14 at 18:41

This is kind of crude and bulky, but it should give you something to work with:

#include <vector>
#include <string>
#include <sstream>
#include <iostream>
#include <stdio.h>
#include <stdlib.h>

using namespace std;

int main() {
    std::cout << "Enter two numbers (0 0 to exit): ";

    string num1;
    while (true) {
        getline(cin, num1);

        string buf;
        stringstream ss(num1);
        vector<string> tokens; // Create vector to hold the two numbers (separately)

        // Split the two numbers (by the spaces)
        while (ss >> buf)
            tokens.push_back(buf);

        cout << "Adding " + tokens[0] << " and " << tokens[1] << endl;

        int sum = atoi(tokens[0].c_str()) + atoi(tokens[1].c_str());

        cout << 0 + sum;

        if (num1.empty()) {

            break;
    }
}

}

score 0 · Answer 3 · answered Mar 26 '19 at 17:34

Another example:

For this you can do:

int a, b;
while(cin >> a >> b , !(a == 0 && b == 0)){
    cout << a+b;
    // any logic for input
}

and for this input:

2
1 2 3 4 5
2 2 2

with c++ can be some tricky

vector<vector<int> > data;
int n;  cin >> n;
for(int i = 0; i < n; ++i)
    data.push_back(read_vector_line());

the tricky function here is read_vector_line. It's something like this:

vector<int> read_vector_line()
{
    vector<int> ans;
    string s;
    getline(cin, s);
    // the below line is necessary sometimes for online judges
    // getchar();
    int num = 0;
    for(int i = 0; i < s.size(); ++i)
    {
        char c = s[i];
        if(c == ' ')
        {
            ans.push_back(num);
            num = 0;
        }
        else
        {
            num = num*10 + (c-'0');
        }
    }
    return ans;
}

I'm not sure if this code compiles correctly. I left you the idea because I did not have any C++ compiler

How to read multiple lines from user in C++?

3 Answers3