---

#include <stdio.h>

int main()
{
	int a = 100;
	int * pa = &a;//pa是专门用来存放地址（指针）的，这里的pa就被称为指针变量
	char* pc = &a;

	//指针变量在32为平台下是4个字节
	//指针变量在64为平台下是8个字节

	//int arr[10];
	//printf("%p\n", &a);

	return 0;
}

int main()
{
	printf("%d\n", sizeof(char*));
	printf("%d\n", sizeof(short*));
	printf("%d\n", sizeof(int*));
	printf("%d\n", sizeof(long*));
	printf("%d\n", sizeof(float*));
	printf("%d\n", sizeof(double*));

	return 0;
}

指针类型的意义

int main()
{
	int a = 0x11223344;//0x开头的是16进制数字
	char* pa = &a;
	*pa = 0;
	return 0;
}

指针类型决定了指针解引用操作的权限

int main()
{
	int a = 0x11223344;//0x开头的是16进制数字

	int* pa = &a;
	char* pc = &a;
	printf("%p\n", pa);
	printf("%p\n", pc);

	printf("%p\n", pa+1);
	printf("%p\n", pc+1);

	return 0;
}

野指针
int main()
{
	int* p;//局部变量不初始化的时候，内容是随机值
	*p = 20;
	printf("%d\n", *p);

	return 0;
}

int* test()
{
	int a = 110;
	return &a;
}

int main()
{
	int* p = test();
	printf("%d\n", *p);

	return 0;
}

int main()
{
	int a = 10;
	int* p = &a;

	int* ptr = NULL;//ptr是一个空指针，没有指向任何有效的空间。这个指针不能直接使用
	//int* ptr2;//野指针

	if (ptr != NULL)
	{
		//使用
	}

	return 0;
}

int main()
{
	int arr[10] = { 0 };
	//不使用下标访问数组
	int* p = &arr[0];
	int i = 0;
	int sz = sizeof(arr) / sizeof(arr[0]);
	for (i = 0; i < sz; i++)
	{
		*p = i;
		p++;//p = p+1
	}
	p = arr;
	for (i = 0; i < sz; i++)
	{
		printf("%d ", *(p + i));//p+i
	}

	/*for (i = 0; i < sz; i++)
	{
		printf("%d ", arr[i]);
	}*/

	return 0;
}

int arr[10]
int* p = arr;
*(p+i) == arr[i]

int main()
{
	int arr[10] = { 1,2,3,4,5,6,7,8,9,10 };
	int i = 0;
	int *p = arr;
	for (i = 0; i < 10; i++)
	{
		printf("%d ", arr[i]);//[] 操作符
		printf("%d ", *(p+i));//[] 操作符
	}

	//2+3 --> 3+2
	//arr[i] --> i[arr]
	return 0;
}

地址-地址
指针-指针

int main()
{
	int arr[10] = { 0 };
	printf("%d\n", &arr[9] - &arr[0]);//?
	printf("%d\n", &arr[0] - &arr[9]);//?

	return 0;
}

int main()
{
	int arr[10] = { 0 };
	char ch[5] = {0};
	//指针和指针相减的前提是：两个指针指向了同一块空间
	printf("%d\n", &ch[4] - &arr[0]);//err

	return 0;
}

int my_strlen(char* s) 
{
	int count = 0;
	while (*s != '\0')
	{
		count++;
		s++;
	}
	return count;
}

int my_strlen(char* s)
{
	if (*s == '\0')
		return 0;
	else
		return 1 + my_strlen(s + 1);
}

int my_strlen(char* s) 
{
	char* start = s;
	while (*s != '\0')
	{
		s++;
	}
	return s - start;
}

int main()
{
	char arr[] = "abcdef";
	int len = my_strlen(arr);
	printf("%d\n", len);

	return 0;
}

int my_strlen(char* s)
{
	char* start = s;
	while (*s)//a b c d e f \0->0
	{
		s++;
	}
	return s - start;
}

int my_strlen(char* s)
{
	char* start = s;
	while (*s++);
	return s - start -1;
}

int main()
{
	char arr[] = "abcdef";
	int len = my_strlen(arr);
	printf("%d\n", len);

	return 0;
}