内部static变量的一个倒子，为什么说它用的好？
书上说：
Consider the problem of writing a function month_name(n), which returns a pointer to a character string containing the name of the n?th month. This is an ideal application for an internal static array. month_name contains a private array of character strings, and returns a pointer to the proper one when called. This section shows how that array of names is initialized.
The syntax is similar to previous initializations:
/* month_name: return name of n?th month */
char *month_name(int n)
{
static char *name[] = {
"Illegal month",
"January", "February", "March",
"April", "May", "June",
"July", "August", "September",
"October", "November", "December"
};
return (n < 1 || n > 12) ? name[0] : name[n];
}
static char *name[] = {
"Illegal month",
"January", "February", "March",
"April", "May", "June",
"July", "August", "September",
"October", "November", "December"
};
//去掉static，没有太多区别，不占函数的栈空间
