Line 13
std::cout << "Enter first integer: "; // prompt user for data
displays Enter first integer:
followed by a space. This message is called a prompt because it directs the user to take a specific action. We like to pronounce the preceding statement as “std::cout
gets the string "Enter first integer: "
.” Line 14
std::cin >> number1; // read first integer from user into number1
uses the standard input stream object cin (of namespace std
) and the stream extraction operator, >>, to obtain a value from the keyboard. Using the stream extraction operator with std::cin
takes character input from the standard input stream, which is usually the keyboard. We like to pronounce the preceding statement as, “std::cin
gives a value to number1
” or simply “std::cin
gives number1
.”
When the computer executes the preceding statement, it waits for the user to enter a value for variable number1
. The user responds by typing an integer (as characters), then pressing the Enter key (sometimes called the Return key) to send the characters to the computer. The computer converts the character representation of the number to an integer and assigns (i.e., copies) this number (or value) to the variable number1
. Any subsequent references to number1
in this program will use this same value.
The std::cout
and std::cin
stream objects facilitate interaction between the user and the computer.
Users can, of course, enter invalid data from the keyboard. For example, when your program is expecting the user to enter an integer, the user could enter alphabetic characters, special symbols (like # or @) or a number with a decimal point (like 73.5), among others. In these early programs, we assume that the user enters valid data. As you progress through the book, you’ll learn various techniques for dealing with the broad range of possible data-entry problems.