例のアレ

stap.cc

#include <iostream>
#include <random>

auto main() -> int {
  std::mt19937 rd{std::random_device()()};
  std::uniform_int_distribution<const char> stuff('A', 'Z');

  unsigned long long int cnt;
  std::string cell;

  for (cnt = 0; cell != "STAP"; ++cnt) {
    // create new cell
    cell.assign({stuff(rd), stuff(rd), stuff(rd), stuff(rd)});

    std::cout << cell << "細胞 ";
  }

  std::cout << std::endl;
  std::cout << cnt << "回目で陽性かくにん☆" << std::endl;
}