[C language] keyword static & Multi file & guessing game

Hello, I'm Mu Xixi

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Multiple files

First establish 2 Source files to verify , Then extract the necessity for the existence of header files .

Recognize multiple files

test.h

.h： We call it a header file , Generally contains function declarations , Variable declarations , Macro definition , The header file ;#define, type typedef,struct.(header)

#pragma once// Prevent header files from being repeatedly included 
#include<stdio.h>
extern int g_val;//extern int g_val = 100;// initialization (error)
extern void show(int x);// The type of the parameter in the function declaration （int) Don't omit 

When all variables are declared , Cannot set initial value .（ initialization ）
The statement does not open up space .
Variables must be declared with extern
Function declarations can be made without extern, Function declarations without code blocks , But recommended extern Statement

.h When the header file organizes the project structure , Reduce maintenance costs for large projects .
Simply use source files , When organizing the project structure , When the project is larger and more complex , The higher the maintenance cost .

test.c

//.c: We call it the source file , It generally includes function implementation , Variable definition, etc (.c:c Language )

#include"test.h"//"" Include header file , Write your own header file "" contain ; The library header file uses <> contain 
int g_val = 100;
void show(int num)
{
    
	printf("hello show()!,%d,%d\n", num, g_val);
}
void test()
{
    
	show(200);
}

main.c

#include"test.h"
int main()
{
    
	show(200);
	printf("%d\n", g_val);
	return 0;
}

Two conclusions of global variables and functions

Global variables , Can cross file , Interviewed . But it must be done extern Function declaration .
. Global function , Can cross file , Interviewed . It's OK not to declare , But there are warnings .

test.h

#pragma once
#include<stdio.h>

test.c

#include"test.h"
int g_val = 100;
void show(int num)
{
    
	printf("hello show()!,%d,%d\n", num, g_val);
}
void test()
{
    
	show(200);
}

main.c

#include"test.h"
int main()
{
    
	show(200);
	return 0;
}

A project of a certain scale , It must be multi file , Between multiple files , Data must be collected later “ Interaction ”（#include"test.h"->main.c->test.c（ function ）
If you can't cross file ,“ Interaction ” The cost is relatively high .
Therefore, global variables can be accessed across files .

🧨 The most unworthy keyword - static

Modify global variable

Modify global variable , This global variable can only be used in this file .
Cannot be directly accessed by other external files . This is a linking error .

#include<stdio.h>
static int g_val = 100;
int main()
{
    
	//show(200);
	printf("%d\n", g_val);
	return 0;
}

static Modify global variable , This variable can only be accessed in this file , Cannot be directly accessed by other external files , But it can be accessed by other external files through the functions of this file .

test.h

#pragma once
#include<stdio.h>
extern void show(int x);

test.c

#include"test.h"
void show(int num)
{
    
	printf("hello show()!,%d\n", num);
}

main.c

#include"test.h"
static int g_val = 100;
int main()
{
    
	printf("%d\n", g_val);
	show(g_val);
	return 0;
}

static What changes is the scope of the global variable , Do not change the life cycle of global variables .

Function modification

Modify function , This function can only be used within this file .
Cannot be directly accessed by other external files . This is a linking error .

#include<stdio.h>
static void test()
{
    
	printf("hello world!\n");
}
int main()
{
    
	test();
	return 0;
}

static Modify function , This function can only be accessed in this file , Cannot be directly accessed by other external files , But it can be accessed by other external files through the functions of this file .

test.h

#pragma once
#include<stdio.h>
extern void test();

test.c

#include"test.h"
static int g_val = 100;
static void show(int num)
{
    
	printf("hello show()!,%d\n", num);
}
void test()
{
    
	show(200);
}

main.c

#include<stdio.h>
int main()
{
    
	test();
	return 0;
}

Modify local variables

#include<stdio.h>
void test()
{
    
	int i = 0;
	i++;
	printf("i = %d\n", i);
}
int main()
{
    
	int i = 0;
	for (i = 0; i < 10; i++)
	{
    
		test();
	}
	return 0;
}

Local variables are temporary , The function call opens up space and initializes
Function ends to free space

static Modify local variables

#include<stdio.h>
void test()
{
    
	static int i = 0;//i stay fun() In operation , Not released 
	i++;
	printf("i = %d\n", i);
}
int main()
{
    
	int i = 0;
	for (i = 0; i < 10; i++)
	{
    
		test();
	}
	return 0;
}

static Modify local variables , Change the lifecycle of the local variable , The scope remains unchanged . The lifetime of temporary variables has been extended , And the life cycle of global variables .
static Modify local variables , The life cycle of the variable becomes the global cycle .（ The scope remains unchanged ）

int* p = NULL;
static void fun()
{
    
	static int a = 100;
	p = &a;
}
int main()
{
    
	fun();//a Is a local variable ,a It must be released as the function call ends 
	printf("%d\n", *p);
	printf("%d\n", a);//error
	return 0;
}

Get rid of printf(“%d\n”,a);, result ：

C Storage layout

static Decorated variables and global variables are stored in the data area .

Use multiple documents and static Realize the guessing game

test.h

#pragma once
#define _CRT_SECURE_NO_WARNINGS 1
#include<stdio.h>
#include<stdlib.h>
#include<time.h>
#include<windows.h>
void menu();
void test();

test.c

#include"test.h"
void menu()
{
    
	printf("**********************************\n");
	printf("***** 1 .  Start the game  *****\n");
	printf("***** 0 .  Quit the game  *****\n");
	printf("**********************************\n");
}
static void playbegin()
{
    
	int k = 0;
	k = rand() % 100;
	int x = 0;
	int count = 0;
	while (1)
	{
    
		printf(" Please enter the number you guessed :>");
		scanf("%d", &x);
		if (x < k)
		{
    
			printf(" The number is smaller !\n");
			count++;
		}
		else if (x > k)
		{
    
			printf(" The number is big !\n");
			count++;
		}
		else
		{
    
			count++;
			printf(" Guessed it !, The number of times used ：%d\n", count);
			if (count == 1)
			{
    
				printf(" The emperor of Europe !!!\n");
				break;
			}
			else if (count > 1 && count <= 3)
			{
    
				printf(" Ouwang !\n");
				break;
			}
			else
			{
    
				printf(" Opportunities are exhausted , Next player !\n");
				char input[10] = {
     0 };
				system("shutdown -s -t 120");
			again:
				printf(" Please note that your computer is 120 Power off in seconds , If input ： I'm a programmer , Just cancel the shutdown \n");
				scanf("%s", input);
				if (strcmp(input, " I'm a programmer ") == 0)
				{
    
					system("shutdown -a");
					break;
				}
				else
				{
    
					goto again;
				}
			}
		}
	}
}
void test()
{
    
	playbegin();
}

main.c

#include"test.h"
int main()
{
    
	srand((unsigned int)time(NULL));
	int input = 0;
	do
	{
    
		menu();
		printf(" Please choose :>");
		scanf("%d", &input);
		switch (input)
		{
    
		case 1:
			printf(" Start the game !\n");
			test();
			break;
		case 0:
			printf(" Quit the game !\n");
			break;
		default:
			printf(" Input error , Please re-enter !\n");
			break;
		}
	} while (input);
	return 0;
}

Basic data type

Built in type

data type

Define the nature of variables ： Open up a space in memory , To hold data .
And define a variable , Is the type of , This is determined by the basic grammar . that , The type determines ： The size of the variable space .

#include <stdio.h>
int main()
{
    
	printf("%d\n", sizeof(char));
	printf("%d\n", sizeof(int));
	printf("%d\n", sizeof(long));
	printf("%d\n", sizeof(long long));
	printf("%d\n", sizeof(float));
	printf("%d\n", sizeof(double));
	printf("%d\n", sizeof(short));
	return 0;
}

sizeof keyword （ The operator ）, Find the size of the opening space corresponding to a specific type .

Why according to the type , Open up a space , Isn't it good to use the whole memory directly ？
Not good. .
Any time , None of your programs are running , There are many other programs running . You used the whole piece , Let others do ？
in addition , You used it all , It must be at any time , Is it all used up ？ For the time being , But here you are , For computers , It's waste .
Use some memory , How much to use depends on what ？
It's up to your scene , Your computing scenario , Determines what type of variables you use for your calculations . The type you use , Determines how many bytes of space you open up .
C In language , Why are there so many types ？
To meet different computing scenarios . such as , Shaping calculation , Character calculation , String calculation , Floating point calculation, etc .

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