Types, variables and input

C++ is statically typed and close to the hardware, so types have fixed sizes and real limits. An int is usually 32 bits and cannot go past about 2.1 billion. Going past that limit is integer overflow.

For a signed int it is undefined behaviour, meaning the language promises nothing, so it is not a wraparound you can rely on. double holds decimals, bool holds true or false, char holds a single byte and std::string holds text.

Always initialise variables, ideally with braces, as in int count{0}. An uninitialised local variable holds garbage: whatever was in that memory before. Integer division cuts off the decimal part, so 7 / 2 is 3.

auto lets the compiler work out a type, which is then fixed. Read user input with std::cin >> x and check that it worked, because typing "abc" into an int puts cin into a failed state.