#include <iostream>

int* positive_or_missing(int& value) {
    if (value > 0) {
        return &value;
    }
    return nullptr;
}

int main() {
    int value{6};
    int* p{positive_or_missing(value)};
    if (p != nullptr) {
        std::cout << *p << '\n';
        value = 9;
        std::cout << *p << '\n';
    }
    int zero{0};
    int* absent{positive_or_missing(zero)};
    if (absent == nullptr) {
        std::cout << "missing" << '\n';
    }
    return 0;
}