Input in C++

In C++, you can receive input from the user using the standard input stream std::cin. This allows your program to become interactive by accepting values at runtime — such as a user’s name, age, or choices.

What is `cin`?

cin stands for console input. It is part of the standard input/output library (iostream) and is used to take input from the keyboard.

Syntax

std::cin >> variable_name;

The >> operator is called the extraction operator, and it extracts data from the input stream (cin) and stores it in the provided variable.

Input for Different Data Types

Let’s explore how to take input for different data types using cin.

1. Integer Input

input_int.cpp

#include <iostream>
 
int main() {
    int age;
    std::cout << "Enter your age: ";
    std::cin >> age;
    std::cout << "You entered: " << age << std::endl;
    return 0;
}

2. Float Input

input_float.cpp

#include <iostream>
 
int main() {
    float temperature;
    std::cout << "Enter the temperature: ";
    std::cin >> temperature;
    std::cout << "Temperature: " << temperature << std::endl;
    return 0;
}

3. Double Input

input_double.cpp

#include <iostream>
 
int main() {
    double price;
    std::cout << "Enter the price: ";
    std::cin >> price;
    std::cout << "Price: " << price << std::endl;
    return 0;
}

4. Character Input

input_char.cpp

#include <iostream>
 
int main() {
    char grade;
    std::cout << "Enter your grade: ";
    std::cin >> grade;
    std::cout << "Grade entered: " << grade << std::endl;
    return 0;
}

Note: cin reads only a single character when reading into a char.

5. Boolean Input

input_bool.cpp

#include <iostream>
 
int main() {
    bool isAvailable;
    std::cout << "Is the item available? (1 for Yes, 0 for No): ";
    std::cin >> isAvailable;
    std::cout << "Availability: " << isAvailable << std::endl;
    return 0;
}

In C++, true is represented as 1 and false as 0.

6. String Input (Single Word)

input_string_word.cpp

#include <iostream>
 
int main() {
    std::string name;
    std::cout << "Enter your name: ";
    std::cin >> name;
    std::cout << "Hello, " << name << "!" << std::endl;
    return 0;
}

When using cin with std::string, it reads only one word, stopping at the first whitespace.

7. String Input (Full Line)

Use std::getline() to read an entire line of input, including spaces.

input_string_line.cpp

#include <iostream>
#include <string>
 
int main() {
    std::string fullName;
    std::cout << "Enter your full name: ";
    std::getline(std::cin, fullName);
    std::cout << "Welcome, " << fullName << "!" << std::endl;
    return 0;
}

Special Case: Using `getline()` After `cin`

If you use cin before getline(), a leftover newline character (\n) may remain in the input buffer. Use std::cin.ignore() to handle this.

cin_getline_combo.cpp

#include <iostream>
#include <string>
 
int main() {
    int age;
    std::string name;
 
    std::cout << "Enter your age: ";
    std::cin >> age;
 
    std::cin.ignore(); // Clears the newline from buffer
 
    std::cout << "Enter your full name: ";
    std::getline(std::cin, name);
 
    std::cout << "Hello " << name << ", age " << age << std::endl;
    return 0;
}

Multiple Inputs at Once

You can input multiple values in one line by chaining variables with the >> operator.

multi_input.cpp

int a, b;
std::cin >> a >> b;

Input: 5 10 Output: a = 5, b = 10

Input Practice Problems

Practice 1: Sum of Two Integers

sum_two_ints.cpp

#include <iostream>
 
int main() {
    int x, y;
    std::cout << "Enter two numbers: ";
    std::cin >> x >> y;
    std::cout << "Sum: " << x + y << std::endl;
    return 0;
}

Practice 2: Calculate Area of Rectangle

area_rectangle.cpp

#include <iostream>
 
int main() {
    float length, width;
    std::cout << "Enter length and width: ";
    std::cin >> length >> width;
    std::cout << "Area: " << length * width << std::endl;
    return 0;
}

Practice 3: Read and Display Name and Age

name_age_input.cpp

#include <iostream>
#include <string>
 
int main() {
    std::string name;
    int age;
 
    std::cout << "Enter your name: ";
    std::getline(std::cin, name);
 
    std::cout << "Enter your age: ";
    std::cin >> age;
 
    std::cout << "Hello " << name << ", Age: " << age << std::endl;
    return 0;
}

Summary

Input Method	Usage Example	Notes
`std::cin >> var`	`std::cin >> age;`	For numbers, characters, single-word strings
`std::getline()`	`std::getline(std::cin, name);`	For full-line string input
`cin >> a >> b`	`std::cin >> a >> b;`	Multiple inputs in one line
`cin.ignore()`	`std::cin.ignore();`	Used before `getline()` after `cin`

Taking user input is essential for making interactive programs. It’s a key building block for anything from a simple calculator to full-fledged applications.

Constants Output