Output, Input, and the Grading Convention

Chaining output

<< chains naturally, which is how you format small messages:

#include <iostream>
#include <string>

int main() {
    std::string name = "Linh";
    int age = 20;
    std::cout << "Name: " << name << ", age: " << age << '\n';
    return 0;
}

Output:

Name: Linh, age: 20

Note that name and age are values — cout knows how to print strings, ints, doubles, and more without any format codes.

Reading input with std::cin

std::cin is the mirror image: it reads from the keyboard into a variable:

std::string name;
int age;
std::cin >> name >> age;   // >> reads, << writes

>> skips leading whitespace and stops at the next space or newline. Input makes programs interactive — try it locally on your machine. Reading input is also where beginners meet their first state bug: reading into the wrong variable type silently fails (age stays at 0). cin >> x followed by checking if (std::cin.fail()) is the honest first lesson in validation, which we develop properly in later modules.

Why graded challenges do not use std::cin

On this platform, graded runs execute your code automatically in a sandbox — nobody is typing at a keyboard. So the grading convention is:

1. Write functions with parameters and return values — tests call them directly, e.g. add(2, 3) must return 5.
2. Or write a void program() that prints something — the test captures what it printed and checks the text.

Lessons and ungraded exploration can still use cin; the sandbox simply replaces it with a clear error during graded runs, exactly like the platform already does for Python. This keeps every challenge automatic, objective, and identical for every learner — in both English and Vietnamese.

The boilerplate you will see

Many challenges pre-fill this shape in the editor:

#include <iostream>

void program() {
    // your code here
}

int main() {
    program();
    return 0;
}

You fill in program(); the harness handles the rest. When a challenge grades a function instead, the boilerplate contains that function's empty shell.