C Language Learning notes-7. Functions

first, the use of functions

1. Each function must be defined before it is used

Example: void function (); With semicolons

int main () {...}

void Add () {...} No semicolon

2. file contains processing:

#include < file name > Find in the directory where the library function header file is located (Standard way)

#include "file name" is located in the current working directory, if not, use the standard method

3. Invocation of functions

Formal parameters: The parameter specified when defining a function

Arguments: Parameters that are specified when a function is called

Note: C language rules can only be passed to arguments by formal parameters

second, the function of the scope of the variable

1. The scope of the local variable is the entire function (including the main function) where it resides

Formal parameters can be considered as local variables

2. Scope of global variables: starting from the position where the variable is defined, to the end of the program

If the global variable has the same name as a local variable in the same source file, the global variable will be masked within the scope of the local variable.

3. Invocation of the function:

Control Flow: The order in which statements are executed

Data flow: The process by which data flows between functions when a function call occurs and ends, such as the passing of parameters, the return

Third, the implementation of the function call process

1. Memory distribution of the process

Operating system
Code
Data segment	Where the compiler stores string constants
Heap	Memory space primarily used for dynamic applications
Stack S1	When a function is called, the system automatically allocates a block in the stack space
S2	Domain gives this function, which holds information such as formal parameters and local variables
......
Global variables

2. Global variables are initialized to 0

four, array and function parameters

1. Function definition: double averagee (int a[], int n) {...}

Function call: Average (score, n);

Note: Data types must be consistent

Because the shape parameter group name is essentially a pointer, it can be defined without specifying a size

Because the array name does not have length information, you need to add a parameter to pass the length of the array

v. Storage properties of Variables

1. Storage type:

Auto (automatic type)	Default local variables, which belong to the default type
Register (registers type)	stored in the CPU register, advantages: High efficiency, disadvantage: Few, only for the int type
Static (quiescent type)	Properties: Global life, local visibility, inheritance
extern (external type)	is not a variable definition, just extends the scope of an external variable (scope: The variable definition position to the end of the source file, and other extern instructions)

C Language Learning notes-7. Functions