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//  Xiuxianjie black market ,1 Class to 8 The price of level monster 
int prices[8] = { 100, 200, 500, 800, 1000, 2000, 5000, 10000 };

int* p = &prices[0]; //prices;

for (int i = 0; i < 8; i++) {
	printf(" The first %d The price of level 1 monster is ：%d  Lingshi \n", i + 1, p[i]);  // Use pointers in the form of arrays 
}

Summary ： For the pointer p, The compiler the p[i] Understood as a ： *(p+i)

The legal use of arrays as pointers

//  Xiuxianjie black market ,1 Class to 8 The price of level monster 
int prices[8] = { 100, 200, 500, 800, 1000, 2000, 5000, 10000 };

*prices = 150;  //  Arrays are used with pointers 

printf("%d\n", prices[0]); // 150

Illegal use of arrays as pointers

//  Xiuxianjie black market ,1 Class to 8 The price of level monster 
int prices[8] = { 100, 200, 500, 800, 1000, 2000, 5000, 10000 };

int x;
prices = &x;  // Array names cannot point to other locations , Similar to a “ Special constant pointer ”

Arrays and pointers “ size ” The difference between

//  Xiuxianjie black market ,1 Class to 8 The price of level monster 
int prices[8] = { 100, 200, 500, 800, 1000, 2000, 5000, 10000 };

int* p = prices;

printf("%d, %d", sizeof(p), sizeof(prices)); 
//  Output  4,32  perhaps  8,32 
//  stay 32 Bit system (x86),  Pointer occupied  4 Bytes of memory 
//  stay 64 Bit system (x64),  Pointer occupied  8 Bytes of memory

Array name , What is it

//  Xiuxianjie black market ,1 Class to 8 The price of level monster 
int prices[8] = { 100, 200, 500, 800, 1000, 2000, 5000, 10000 };

// 1.  The value of the array name , That's the number... Of the array 0 Addresses of members 
printf("%x, %x\n", prices, &prices[0]);

// 2.  Access to data , Array name , Similar to a constant pointer ,  You can't change the direction 
//  here ,p and prices Very similar 
int* const p = &prices[0];  //const The usage of will be explained in detail later 

// 3.  For memory size , Arrays and types are different 
printf("%d, %d", sizeof(p), sizeof(prices));

6.2 Pointers and const

In the monster black market of Xiuxian world , Use the pointer to browse the black market , coordination const, You can get different results .

Free pointer - Look around , Violent bargaining

//  Xiuxianjie black market ,1 Class to 8 The price of level monster 
int prices[8] = { 100, 200, 500, 800, 1000, 2000, 5000, 10000 };
int* p = prices;

p += 2;		//  Change direction 
*p -= 100;  // Forcibly change the price 
printf("%d\n", *p); //400

pointer to const - Buddhism department goes shopping in the black market , Just look, not bargain

//  Xiuxianjie black market ,1 Class to 8 The price of level monster 
int prices[8] = { 100, 200, 500, 800, 1000, 2000, 5000, 10000 };
const int* p = prices;
	
p += 2;    // You can change p The direction of 
*p -= 100; // Compile failed ！  Cannot change the content pointed

Constant pointer - Look at a monster , Just for it

//  Xiuxianjie black market ,1 Class to 8 The price of level monster 
int prices[8] = { 100, 200, 500, 800, 1000, 2000, 5000, 10000 };
int * const p = prices;

p += 2;		// Compile failed ！ You can't change the direction 
*p -= 50;	// You can bargain （ Can change the data pointed ）

Constant pointer to constant - A dedicated customer who doesn't need money

//  Xiuxianjie black market ,1 Class to 8 The price of level monster 
int prices[8] = { 100, 200, 500, 800, 1000, 2000, 5000, 10000 };
const int * const p = prices;

p += 2;		// Compile failed ！ You can't change the direction 
*p -= 50;	// Compile failed ！ Don't bargain , The data pointed to cannot be changed

6.3 Pointer to array

Let's analyze the longevity of immortals at all levels , By the way, master the usage of pointing to arrays .

Lower realm

Qi training period （ Absorb the aura of heaven and earth , Into the body into the element force , Longevity can reach a hundred years , It can fly in a short time ）
Foundation period （ Dantian is liquid , Kepigu , Up to 200 years old , Cannot escape the light , Can fly a sword for a long time ）
Jindan period （ There are regular round solid Dan yuan in the Dantian , Opened Valley , Longevity can reach 500 years , You can fly by light ）
Primipara （ Broken pills become babies , Longevity can reach thousands of years , Light flight , Broken body baby can teleport ）

Upper realm

The transformation period （ The body is doubled , Yuanying transits to Yuanshen , More than 2000 years , Master Yuan Li , Can break Yuan Ying's blink ）
The period of deficiency （ Shouyuan can reach nearly 5000 years old , Yuanying in the body turns into Yuanshen , Return to the virtual body , Into separate bodies or multiple separate bodies ）
Syncytial stage （ Separation and noumenon are one , To return to simplicity , You can break thousands of incarnations of refining emptiness , Longevity can last for tens of thousands of years ）
Mahayana （ Up to 20000 years , Skillfully use or create their own magic powers , The mana body is ready to fly , Chen is a monk with great power ）

Definition and basic use of pointers to arrays

int ages[2][4] = {
	100, 200, 500,  1000,   //ages[0]   In the lower realm 4 An array of levels of life 
	2000,5000,10000,20000   //ages[1]   In the upper realm 4 An array of levels of life 
};

int(*p)[4]; 
// Defines a pointer to an array p
//p Can only point to :  contain 4 Members , Every member is int An array of types 
// Pay attention to the grammar ,* Must be in ( ) Inside 

p = &ages[0]; //ages

//  Through the pointer to the array , To access the members in the array 
for (int i = 0; i < 4; i++) {
	printf("%d ", (*p)[i]);  // p[0][i]
}

//  The size of the pointer to the array 
printf("\n %d %d \n", sizeof(p), sizeof(*p));

Addition and subtraction of pointers to arrays

int ages[2][4] = {
	100, 200, 500,  1000,   //ages[0]   In the lower realm 4 An array of levels of life 
	2000,5000,10000,20000   //ages[1]   In the upper realm 4 An array of levels of life 
};

int(*p)[4] = &ages[0]; //ages

p++; // p Points to the next array ！
printf("%d\n", (unsigned int)(p + 1) - (unsigned int)p); //16

for (int i = 0; i < 4; i++) {
	printf("%d ", (*p)[i]);  // 2000
}

6.4 The parameters of the function pass an array

The parameters of the function pass a one-dimensional array

Calculation 1-8 The average price of level monster .

#include <stdio.h>

int calcAveragePrice1(int p[8]) {
	//  Particular attention ： here  p  Arrays are not real arrays , It's actually a pointer  int *p
	printf("%d\n", sizeof(p));

	int s = 0;
	for (int i = 0; i < 4; i++) {
		s += p[i];
	}
	return s / 4;
}

int calcAveragePrice2(int p[], int n) {
	int s = 0;
	for (int i = 0; i < 4; i++) {
		s += p[i];
	}
	return s / 4;
}

int calcAveragePrice3(int *p, int n) {
	int s = 0;
	for (int i = 0; i < 4; i++) {
		s += p[i];
	}
	return s / 4;
}

int main(void) {
	//  Xiuxianjie black market ,1 Class to 8 The price of level monster 
	int prices[8] = { 100, 200, 500, 800, 1000, 2000, 5000, 10000 };
	
	//  Calculation 1-8 The average price of level monster 
	printf("%d\n", calcAveragePrice1(prices)); //ages;
	printf("%d\n", calcAveragePrice2(prices, 8)); //ages;
	printf("%d\n", calcAveragePrice2(prices, 8)); //ages;

	return 0;
}

The parameters of the function pass a two-dimensional array （4 Ways of planting ）

Calculate the average life span of monks at all levels .

#include <stdio.h>

int calcAverageAge1(int ages[2][4]) {
	//  Particular attention ： here  ages  Not a real two-dimensional array 
	//  It's actually a pointer to a one-dimensional array  int (*ages)[4]
	printf("%d\n", sizeof(*ages));

	int s = 0;
	for (int i = 0; i < 2; i++) {
		for (int j = 0; j < 4; j++) {
			s += ages[i][j];
		}
	}

	return s / (2 * 4);
}

int calcAverageAge2(int ages[][4], int n) {
	//  Particular attention ： here ages  Arrays are not real arrays 
	//  It's actually a pointer to a one-dimensional array  int (*ages)[4]
	printf("%d\n", sizeof(*ages));

	int s = 0;
	for (int i = 0; i < n; i++) {
		for (int j = 0; j < 4; j++) {
			s += ages[i][j]; // *(*(ages+i) + j)
		}
	}

	return s / (2 * 4);
}


int calcAverageAge3(int(*ages)[4], int n) {
	printf("%d\n", sizeof(*ages));

	int s = 0;
	for (int i = 0; i < n; i++) {
		for (int j = 0; j < 4; j++) {
			s += ages[i][j]; // *(*(ages+i) + j)
		}
	}

	return s / (2 * 4);
}

int calcAverageAge4(int* ages, int m, int n) {
	int s = 0;
	for (int i = 0; i < m; i++) {
		for (int j = 0; j < n; j++) {
			s += *(ages + i * n + j);
		}
	}

	return s / (2 * 4);
}

int main(void) {
	int ages[2][4] = {
		100, 200, 500,  1000,   //ages[0]   In the lower realm 4 An array of levels of life 
		2000,5000,10000,20000   //ages[1]   In the upper realm 4 An array of levels of life 
	};

	printf("%d\n", calcAverageAge1(ages));
	printf("%d\n", calcAverageAge2(ages, 2));
	printf("%d\n", calcAverageAge3(ages, 2));
	printf("%d\n", calcAverageAge4(ages, 2, 4));
	return;
}

“C Language and C++ in , You can't directly put a two-dimensional array （ Or more multidimensional arrays ）, As a function parameter of general form , You cannot pass a normal multidimensional array to a function .” Quote from 《C Experts programming 》 The first 10 Chapter of 5 section .

But we can use the above example code 4 Two forms to pass two-dimensional arrays .

6.5 Function returns an array

Define a function , Calculate , Returns an array , The array contains the lowest and highest prices of monsters at all levels , And the average price .

int(*calc(int prices[], int n))[3]{
	int s = 0;
	for (int i = 0; i < n; i++) {
		s += prices[i];
	}

	int(*ret)[3]; //  Define a pointer to an array 
	ret = malloc(3 * sizeof(int));
	(*ret)[0] = prices[0];
	(*ret)[1] = prices[n - 1];
	(*ret)[2] = s / n;
	return ret;
}

int main(void) {
	//  Xiuxianjie black market ,1 Class to 8 The price of level monster 
	int prices[8] = { 100, 200, 500, 800, 1000, 2000, 5000, 10000 };
	int(*p)[3] = calc(prices, 8);

	printf(" The lowest price =%d,  The highest price =%d,  The average price =%d", (*p)[0], (*p)[1], (*p)[2]);
	
	return;
}

Use typedef Pointer to array , To optimize ：

typedef int(*threeValueArray_t)[3];

threeValueArray_t calc(int prices[], int n){
	int s = 0;
	for (int i = 0; i < n; i++) {
		s += prices[i];
	}

	int(*ret)[3]; //  Define a pointer to an array 
	ret = malloc(3 * sizeof(int));
	(*ret)[0] = prices[0];
	(*ret)[1] = prices[n - 1];
	(*ret)[2] = s / n;
	return ret;
}

int main(void) {
	//  Xiuxianjie black market ,1 Class to 8 The price of level monster 
	int prices[8] = { 100, 200, 500, 800, 1000, 2000, 5000, 10000 };
	threeValueArray_t p = calc(prices, 8);

	printf(" The lowest price =%d,  The highest price =%d,  The average price =%d", (*p)[0], (*p)[1], (*p)[2]);
	
	return;
}

thus , We have mastered the usage of the pointer in the foundation period , The golden elixir period is about to advance ！