<|im_start|>system
You are a helpful AI assistant.<|im_end|>
<|im_start|>user
Write me a program in C++ to compute the factorial of a number at compile time, using only C++03<|im_end|>
<|im_start|>assistant
Here is a a C++ program that computes a factorial at compile time, that is compliant with the C++03 standard.

```cpp
template<unsigned int N>
unsigned int fac() {
    return fac<N-1>() * N;
};

template<>
unsigned int fac<0>() {
    return 1;
}
```

Using templates and template specialization we define a function fac<N>() which returns fac<N-1>()*N, specializing the case where N = 0 to return 1.<|im_end|>
<|im_start|>user
What are the pros and cons of doing this during compilation instead of runtime?<|im_end|>
<|im_start|>assistant
Pros of computing the factorial at compile time:

Efficiency: The calculation is performed at compile time, so there is no runtime overhead. This means that the program will run faster and use less resources than if the calculation was done at runtime.

Constant value: The result of the calculation is stored as a constant in the program, so it can be easily accessed and used multiple times without having to recompute it.

Improved code readability: By having the result of the calculation available as a constant, the code is more readable and easier to understand.

Cons of computing the factorial at compile time:

Limited flexibility: Since the calculation is performed at compile time, it cannot be changed at runtime. This means that if you need to calculate the factorial for a different number, you will need to recompile the program.

Larger binary size: The factorial calculation is performed at compile time, which means that the result will be included in the binary file. This can lead to a larger binary size and longer compile times.

Limited to constant values: The factorial calculation can only be performed for constant values that are known at compile time. It cannot be used for values that are only known at runtime.<|im_end|>