Reading Input with cin

Asking the user

cout sends things to the screen. Its partner cin (say: “see in”) reads things from the keyboard. Notice the arrows point the other way: >>.

#include <iostream>
using namespace std;

int main() {
    int age;
    cout << "How old are you? ";
    cin >> age;
    cout << "In 10 years you will be " << age + 10 << "\n";
    return 0;
}

Input (what the user types)

16

Output

How old are you? In 10 years you will be 26

Think of it like this: cin >> age is like pouring what the user typed into the age box. The arrows show the direction the data flows: from cin into the variable.

In the examples in this course, the box called Input shows what the user typed. In a real terminal you would see it next to the question.

Reading several values

You can chain >> just like <<. The values can be on one line, separated by spaces, or on separate lines:

#include <iostream>
using namespace std;

int main() {
    int a, b;
    cout << "Enter two numbers: ";
    cin >> a >> b;
    cout << "Their sum is " << a + b << "\n";
    return 0;
}

Input (what the user types)

7 35

Output

Enter two numbers: Their sum is 42

Tip: int a, b; creates two int variables in one line.

Reading a word

#include <iostream>
#include <string>
using namespace std;

int main() {
    string name;
    cout << "What is your name? ";
    cin >> name;
    cout << "Nice to meet you, " << name << "!\n";
    return 0;
}

Input (what the user types)

Arjun

Output

What is your name? Nice to meet you, Arjun!

Common mistake: cin >> stops at the first space. If the user types Arjun Mehta, name only gets Arjun. The next lesson shows how to read a whole line.