Fib_table_cached.cpp

#include <cassert>
#include <iostream>
#include <unordered_map>

class Fibonacci final {
  public:
    static int get(int n) {
      assert(n >= 0);
      if (n == 0 || n == 1) {
        return n; 
      }
      
      static std::unordered_map<int, int> cache;
      auto &result = cache[n];
      if (result == 0) {
        result = get(n-2) + get(n-1);
      }
      return result;
    }
}

int main() {
  int n;
  std::cin >> n;
  stf::cout << Fibonacci.get(n) << std::endl;
  return 0;
}

Or using loop:
assert(n >= 0); static std::unordered_map<int, int> cache; cache[0] = 0; cache[1] = 1; for (int i = 2; i <= n; i++) { cache[i] = cache[i - 2] + cache[i - 1]; } return cache[n];

Or using vector:
static std::vector<int> cache; cache.resize(n+1); ...

Or using only two prev calculated numbers:
int prev = 0; int cur = 1; for (int i = 2; i <= n; i++) { int new_cur = prev + cur; prev = cur; cur = new_cur; } return cur;