cin, cout, and streams

Output and input are two directions of one idea: streams. Let's use both and make a program that responds.

Output: chaining cout

One cout can chain many pieces with << — text, numbers, computed expressions, all flowing out left to right. No format placeholders like C's %d; the stream figures out each type itself. That's a real C++ comfort over C.

Input: cin into variables

std::cin >> reads typed input and stores it. The arrows reverse — data flows from the input into your variable:

#include <iostream>
 
int main() {
    std::string name;
    int age;
 
    std::cout << "Name: ";
    std::cin >> name;         // read a word into name
    std::cout << "Age: ";
    std::cin >> age;          // read a number into age
 
    std::cout << "Hello " << name << ", next year you're "
              << age + 1 << std::endl;
    return 0;
}

cin >> is smart about types: reading into an int parses a number, into a std::string grabs a word. (Our sandbox can't accept live typing, so input examples are shown as code — run them on your own machine to try.)

The symmetry

Remember it by the arrows: they always point the way the data moves.