Modern C++: The Good Parts/The world's response

Now, let's allow the world to return the greeting.

Code

#include <iostream>
#include <string>

int main()
{
	std::string input;
	
	std::cout << "Hello, world!\n";
	
	// Notice the arrows point to the right.
	std::cin >> input;
	std::cout << "The world says: " << input << "\n";
}

Explanation

We have a few new things here.

std::string means that input is a string variable. A variable is a named place in memory to store information. Since it's named, you can refer to it again and again, to put something there or to see what's already there. And as a string variable it can store text - and only text. Other kinds of variables exist, and we'll cover some of those in the next chapter.

// is a line comment, which means everything after it on the same line will be ignored by the compiler.

std::cin has an arrow that points in the opposite direction from the arrows of std::cout, because information is flowing in the opposite direction.

After "The world says: ", there's another arrow, and then another. This just appends more text to the output.

Exercises

• Extend the conversation between your program and the "world". Don't bother with whether the program is responding correctly to what is typed.

Vocabulary

variable

a named place in memory to store information.

line comment

causes the compiler to ignore the rest of a line. Syntax: //