Using cin

As the output from Listing 2.3 demonstrates, the value typed from the keyboard (12) is eventually assigned to the variable carrots. The following statement performs that wonder:

cin >> carrots;

Looking at this statement, you can practically see information flowing from cin into carrots. Naturally, there is a slightly more formal description of this process. Just as C++ considers output to be a stream of characters flowing out of the program, it considers input to be a stream of characters flowing into the program. The iostream file defines cin as an object that represents this stream. For output, the << operator inserts characters into the output stream. For input, cin uses the >> operator to extract characters from the input stream. Typically, you provide a variable to the right of the operator to receive the extracted information. (The symbols << and >> were chosen to visually suggest the direction in which information flows.)

Like cout, cin is a smart object. It converts input, which is just a series of characters typed from the keyboard, into a form acceptable to the variable receiving the information. In this case, the program declares carrots to be an integer variable, so the input is converted to the numeric form the computer uses to store integers.