8、 C scope rules

One 、 introduction

Scope refers to the area where the variable exists , Beyond this area, the variable cannot be accessed , stay C In language , There are three kinds of variable declarations ：

• local variable ： Variables declared in a function , It is unknowable outside the function
• Global variables ： Defined outside the function , It is effective throughout the program cycle , In band function , If local variables and global variables have the same name , Will use local variables
• Formal parameters ： The parameters of the function , Equivalent to a local variable in a function

Two 、 initialization

When the authority variable is defined , The system will not initialize it . When global variables are defined , The system will initialize it by default ：

data type	Initialize defaults
int	0
char	‘\0’
float	0
double	0
pointer	NULL