Political pollsters have completed their root-cause analysis of why they misjudged the results of the early straw polls and caucuses in the 2024 Presidential Race -- it turns out, to fix the problem, all they had to do was ask for the voters' input!
Like we are able to perform character output (std::cout), we are able to perform character input as well. In fact, the two operations look very similar.
Remember what it looks like to print the contents of the variable name to the screen:
#include <iostream>
int main() {
std::string name{"Alexandra"};
std::cout << name;
return 0;
}The output is actually accomplished on line 5:
std::cout << name;As you recall, the << is called the stream insertion operator because we are telling the compiler to "insert" the value of name in to a "stream" of data that is destined for the character output device (usually the console, a name given to computer screens in the earliest days of computing!). Visually, the << is intuitive because it looks like it is "funneling" the value from name to std::cout (which we can think of as the console).
What would happen if we flipped that around? Well, it would seem to follow that we could go in the opposite direction and get values from the stream of data that is coming from the console!
And, yes, we can! To read the user's name from their keyboard input, we use std::cin and >>, the stream extraction operator.
#include <iostream>
int main() {
std::string name{""};
std::cin >> name;
return 0;
}std::cin is pretty powerful! It gives us the power to ask the user for data of a certain type and enforce that condition! Let's see how that works. Say we want to ask the user to enter the number of tires on their car. Well, you can't have half a tire on your car, so the number that they enter must be a whole number -- an int.
#include <iostream>
int main() {
int num_tires_on_car{0};
std::cin >> num_tires_on_car;
return 0;
}Because num_tires_on_car is an int, we can use the value that the user entered (which we subsequently stored in num_tires_on_car) in mathematical expressions wherever we would require an int. Pretty cool!
Later, we will learn how to check whether the user entered a value that is valid for the type that we want. That will give us even more power!
A word is a std::string. If we wanted to write a program that gave a user some positive feedback about their favorite word, it would look something like this:
#include <iostream>
int main() {
std::string favorite_word{""};
// Prompt the user for their input.
std::cout << "Please type your favorite word: ";
// Read in their input.
std::cin >> favorite_word;
std::cout << favorite_word << " is a great word!\n";
return 0;
}First, we are "prompting" the user for their input -- basically, we are asking them for some response. Because we want the prompt to appear on the screen, we are using std::cout and the stream insertion operator. Then we are reading the response that they typed. We are using std::cin and the stream extraction operator. Finally, we are giving the user praise for their choice. We are using the stream insertion operator and std::cout again to make a message appear on the screen!
Here's how it might look if we ran that program (user input in bold).
Please type your favorite word: obscure obscure is a great word!