int a => auto variable
The cost of setting auto variables to 0 would
increase the cost of function calls. C has a very
strong focus on execution speed.
static int a
the global data segment to 0
however, is a one time cost that happens at
start up, and that might be the reason why it is
so in C.
在C 語言中，static variables 預設是0，但在C++ 卻不是這樣，
And to be precise, in C++ however, static
variables are not set to 0, they are set to their
default values... which for native types means 0
=> 結果: 1
Memsetting the global data segment to 0