std::cin
- C++ course
- Beginner
- Lesson 4/116
- 4 min
Learn to read input from the user with std::cin.
std::cin
std::cin is the standard input stream; it reads data from the keyboard. The >> operator writes data from the input stream into a variable. You first declare a variable, then read its value with std::cin >> var;.
For example, after declaring int age;, writing std::cin >> age; stores the number the user types into age. You can then print it with std::cout << age.
std::cin reads up to whitespace or a newline; you can read several values in a row with std::cin >> a >> b;.
Input and output with variables
In a real program, you store the value read by std::cin in a variable, then process and print it with std::cout. A variable is a box that holds a value by name.
In the example below, the age variable holds an integer; the user enters it and the program prints it:
int age = 25;
std::cout << "Age: " << age << std::endl;Here the value is given directly as 25; in a real program it would be read with std::cin >> age;. You will learn variable declaration in detail in the next section.
Practice Print the age
Declare an int age variable and assign it 25 (in a real program you would read it with std::cin >> age;). Then use std::cout to produce the output Age: 25: print the string "Age: ", then the age variable, then std::endl.
Starter code
#include <iostream>
int main() {
// Declare the age variable and assign 25
// Print "Age: " and the age value with std::cout
return 0;
}Sample solution
#include <iostream>
int main() {
// Declare the age variable and assign 25
int age = 25;
// Print "Age: " and the age value with std::cout
std::cout << "Age: " << age << std::endl;
return 0;
}Expected output
Age: 25
Questions and answers
Review the lesson questions together with their answers. To test yourself, solve the lesson interactively.
1 Match the I/O concepts
| Term | Meaning |
|---|---|
std::cin |
Input stream |
>> |
Input operator |
std::cout |
Output stream |
<< |
Output operator |
2 Input operator
std::cin ____ age;std::cin >> age;Explanation: The >> operator reads from the input stream into a variable.
3 What does std::cin do?
- It creates a file
- It prints text to the screen
- It compiles the program
- It reads data from the keyboard Correct answer
Explanation: std::cin is the standard input stream and reads from the keyboard.