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Biến và kiểu dữ liệu
In C++, every variable has a well-defined static type at compile time. This means that once you declare a variable of a certain type, you cannot change its type later.
This approach guarantees maximum performance at runtime and allows the compiler to catch many common errors before the program even runs.
Declaration and Initialization
To declare a variable in C++, you must specify the type first, followed by the name of the variable:
int age; // Declaration without initialization (contains an undefined value!)
age = 25; // Subsequent assignment
Modern Initialization
Modern C++ introduces several forms of initialization. The safest and most uniform is brace initialization (introduced in C++11):
int age = 25; // Classic initialization (C-style)
int score {100}; // Uniform initialization (C++11)
Fundamental Primitive Types
Here are the main data types you will use every day:
| Type | Description | Example |
|---|---|---|
int | Integer numbers (e.g. 1, -42, 0) | int points = 50; |
double | Double-precision floating-point numbers | double price = 19.99; |
char | A single character enclosed in single quotes | char grade = 'A'; |
bool | Boolean values (true or false) | bool isActive = true; |
Complex Objects: std::string
To manage text sequences, the C++ standard library provides the std::string class (defined in the <string> header):
#include <string>
std::string name = "Alice";
Try it yourself
Declare a variable named age of type int with value 30, and print it using std::cout.
Hiển thị gợi ý
Use the syntax `int age = 30;`to declare the variable, then print it with`std::cout << age;`.
Giải pháp khả dụng sau 3 lần thử
Declare a variable named username of type std::string with value 'Alice', and print it using std::cout.
Hiển thị gợi ý
Usa `std::string username = "Alice";` e poi inviala allo stream std::cout.
Giải pháp khả dụng sau 3 lần thử