Shifts and narrowing

Questions 1 to 5 of 7

1. 1. What does this program print? ``cpp #include <iostream> int main() { int a = -21; std::cout << (a >> 2) << " " << (a / 4) << "\n"; } ``

   -5 -5-6 -6-5 -6-6 -5
2. 2. What does this program print? ``cpp #include <iostream> int main() { short s = 30000; s += 5000; std::cout << s << "\n"; } ``

   35000-30536-327682232
3. 3. The program should print sent 300, but it prints sent 44. What is the bug? ``cpp #include <iostream> int main() { unsigned char packets = 0; for (int k = 0; k < 300; ++k) { packets += 1; } std::cout << "sent " << static_cast<int>(packets) << "\n"; } ``

   packets is an unsigned char, which holds 0 to 255. After 256 additions it wraps, and the store keeps only the low 8 bits, so the count is 44.The loop should run 299 times, because the count starts at 1.The static_cast<int> hides the real value, so the printed number is wrong but the count is right.packets should be a short, because += cannot be used on an unsigned char.
4. 4. The program should print total 3, but it prints total 0. What is the bug? ``cpp #include <iostream> int main() { int total = 0; for (int k = 0; k < 10; ++k) { total += 0.3; } std::cout << "total " << total << "\n"; } ``

   The loop should run 3 times, so the total reaches 3.total should be a long, because long can hold fractions.Each += adds 0.3 but stores the result in an int, which drops the fraction, so the total never gets past 0.The literal 0.3 is too small for a double to store, so it is read as 0.
5. 5. True or False: g++ -std=c++20 -Wall warns about the line c += 300; in this program. ``cpp #include <iostream> int main() { char c = 100; c += 300; std::cout << static_cast<int>(c) << "\n"; } ``

   True, because -Wall reports every store that can change a valueFalse, because -Wall prints nothing for this line, and -Wconversion is the flag that warns about it