#include <iostream>
#include <cstdlib>   //for getenv
#include <cstring>   //for strcmp
using namespace std;

int main(int argc, char *argv[], char *envp[])
{
	//Output all the environment variables.

	for (int i {0}; envp[i] != nullptr; ++i) {
		cout << envp[i] << "\n";
	}

	//Output one environment variable.

	const char *const p {getenv("USER")};
	if (p != nullptr) {
		cout << "\n";
		cout << p << "\n";
	}

	if (strcmp(p, "mmeretzky") != 0) {  //if the USER is not mmeretzky
		cerr << "Sorry, only mmeretzky can run this program.\n";
		return EXIT_FAILURE;
	}

	return EXIT_SUCCESS;
}