Your First Program: cout

Saying hello

The first thing every programmer learns is how to show something on the screen. In C++ we use cout (say it: “see out”, short for character output):

#include <iostream>
using namespace std;

int main() {
    cout << "Hello, World!";
    return 0;
}

Output

Hello, World!

The important line is cout << "Hello, World!";

• cout is the screen.
• << means “send to”. Picture an arrow pushing the text into cout.
• The double quotes " " mark text. Text in quotes is called a string.
• The ; (semicolon) ends the instruction, like a full stop ends a sentence.

Remember: Every instruction in C++ ends with a semicolon ;. Forgetting it is the most common beginner mistake.

New lines: endl and \n

cout does not start a new line by itself. Look what happens with two lines:

#include <iostream>
using namespace std;

int main() {
    cout << "Line one";
    cout << "Line two";
    return 0;
}

Output

Line oneLine two

Both pieces end up on the same line! To end a line, send endl (end line) or put \n inside the text. Both do the same job:

#include <iostream>
using namespace std;

int main() {
    cout << "Line one" << endl;
    cout << "Line two\n";
    cout << "Line three" << "\n";
    return 0;
}

Output

Line one
Line two
Line three

Tip: Most programmers use "\n" because it is shorter. Use whichever you like.

Chaining many things together

You can use << many times in one line. Each piece is sent to the screen, one after another. Numbers don't need quotes, and C++ can even do maths for you:

#include <iostream>
using namespace std;

int main() {
    cout << "I am " << 20 << " years old." << "\n";
    cout << "Next year I will be " << 20 + 1 << "\n";
    cout << "5 + 3 = " << 5 + 3 << "\n";
    return 0;
}

Output

I am 20 years old.
Next year I will be 21
5 + 3 = 8

See the difference? "5 + 3 = " is in quotes, so it is printed exactly as written. 5 + 3 has no quotes, so C++ works it out and prints 8.

Special characters

Some characters need a backslash \ in front of them. These are called escape sequences:

#include <iostream>
using namespace std;

int main() {
    cout << "She said \"Hi!\"\n";        // \" puts a quote inside text
    cout << "Name:\tSam\n";              // \t is a tab (a wide space)
    cout << "A backslash: \\\n";         // \\ prints one backslash
    return 0;
}

Output

She said "Hi!"
Name:	Sam
A backslash: \