// test: echo -e '\n\n\n' | calc.exe -n
// test: echo -e '1.5\nsto (2)\n3 + rcl(2) * 4\nsto (5)' | calc.exe | grep -q 9
// test: echo -e '1\nsto (0)\nsto (11)\nrcl (0)\nrcl (11)' | calc.exe | grep -c invalid | xargs test 4 =
// test: echo -e '\n\n\n' | calc.exe -n
// test: echo -e '1.5\nsto (2)\n3 + rcl(2) * 4\nsto (5)' | calc.exe | grep -q 9
// test: echo -e '1\nsto (0)\nsto (11)\nrcl (0)\nrcl (11)' | calc.exe | grep -c invalid | xargs test 4 =