What is the difference between constexpr and const in C++?

Hi everyone! I started learning C++11 and came across the new keyword `constexpr`. Previously I always used `const` to declare immutable variables. But now there's also `constexpr`, and I can't fully understand when to use which. For example, I write this code: ```cpp const int size = 5; int arr[size]; // This works ``` But if I write: ```cpp int get_size() { return 5; } const int size = get_size(); int arr[size]; // Compilation error in older standards! ``` I understand that `const` simply prevents modifying the variable after initialization, but doesn't guarantee the value is known at compile time. At the same time, I see examples with `constexpr`: ```cpp constexpr int square(int x) { return x * x; } constexpr int val = square(5); // Ok, computed at