Types, Variables, and I/O

Variables

int count = 3;
double price = 9.99;
bool ready = true;
char grade = 'A';
std::string name = "Ada";

Initialization style

Prefer brace initialization when practical:

int age{42};
double ratio{0.5};

Output

std::cout << name << " has age " << age << '\n';

Input

int year{};
std::cin >> year;

Example program

#include <iostream>
#include <string>

int main() {
    std::string name;
    int age{};

    std::cout << "Name: ";
    std::getline(std::cin, name);
    std::cout << "Age: ";
    std::cin >> age;

    std::cout << name << " will be " << age + 1 << " next year.\n";
}

Practice ideas

• Read two numbers and print their sum
• Read a name and greet the user
• Print values with labels and units

Type deduction and const

const auto max_retries = 3;
auto price = 19.99;

Use const by default for local values that should not change. Use auto when the initializer already makes the type obvious.

Safer modern text APIs

void greet(std::string_view name) {
    std::cout << "Hello, " << name << '\n';
}

std::string_view avoids copies for read-only text parameters, but it does not own data. The caller must keep the underlying string alive.

Input pitfalls

If you mix std::cin >> value with std::getline, consume the leftover newline first or structure input as full lines and parse afterwards.