comptime/consteval1.cpp

The following code example is taken from the book
C++20 - The Complete Guide by Nicolai M. Josuttis, Leanpub, 2021
The code is licensed under a Creative Commons Attribution 4.0 International License.

---

// raw code

#include <iostream>
#include <array>

constexpr
bool isPrime(int value)
{
  for (int i = 2; i <= value/2; ++i) {
    if (value % i == 0) {
      return false;
    }
  }
  return value > 1;  // 0 and 1 are not prime numbers
}

template<int Num>
consteval
std::array<int, Num> primeNumbers()
{
  std::array<int, Num> primes;
  int idx = 0;
  for (int val = 1; idx < Num; ++val) {
    if (isPrime(val)) {
      primes[idx++] = val;
    }
  }
  return primes;
}

int main()
{
  // init with prime numbers:
  auto primes = primeNumbers<100>();

  for (auto v : primes) {
    std::cout << v << '\n';
  }
}