C++ · Variables, types and I/O

In Python a name can point to anything. In C++ every variable has a static type that is fixed at compile time.

type	typical size	notes
int	4 bytes	about ±2.1 billion
long long	8 bytes	use it for big counts
double	8 bytes	the default floating-point type
char	1 byte	a single character
bool	1 byte	true / false

• auto lets the compiler deduce the type from the initialiser. The type is still static.
• const makes a variable read-only.
• Overflowing a signed integer is undefined behaviour, unlike Python’s unlimited ints. Use long long when values can get big.
• std::cin >> x reads input. I used a std::istringstream below so the example runs without typing anything.

#include <iostream>
#include <sstream>
#include <limits>

int main() {
    const double pi = 3.14159;
    auto count = 42;            // int
    auto ratio = 0.75;          // double
    long long big = 3'000'000'000LL;

    std::cout << "int max: " << std::numeric_limits<int>::max() << '\n';
    std::cout << "big: " << big << ", count: " << count << ", ratio: " << ratio << '\n';
    std::cout << "7/2 = " << 7 / 2 << ", 7.0/2 = " << 7.0 / 2 << '\n';

    std::istringstream in("Sahaj 19");
    std::string name; int age;
    in >> name >> age;
    std::cout << name << " is " << age << ", area of r=2 circle: " << pi * 2 * 2 << '\n';
}

Output:

int max: 2147483647
big: 3000000000, count: 42, ratio: 0.75
7/2 = 3, 7.0/2 = 3.5
Sahaj is 19, area of r=2 circle: 12.5664