C语言中的初阶指针详解

int main()
{
	int a = 10;
	int* pa = &a;
    return 0;
}
//pa是用来存放地址（指针），所以pa是指针变量。

int main()
{
	char* pc = &a;
	*pc = 0;
	return 0;
}

int main()
{
	int a = 10;
	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;
}

int main()
{
    int* p;//局部变量指针未初始化，默认为随机值
    *p = 20;//通过p中存的随机值作为地址，找到一个空间，这个空间不属于我们当前的程序
    //就造成了非法访问，p就是野指针
    return 0;
}

int main()
{
    int arr[10] = 0;
    int i = 0;
    int* p = arr;
    for(i =0; i <= 10; i++)
    {
        *p = i;
        p++;//当指针指向的范围超出数组arr的范围时，p就是野指针
    }
    return 0;
}

int* test()
{
    int a = 10;
    return &a;
}
int main()
{
    int* p = test();
    printf("%d\n",*p);
    return 0;
}

int main()
{
    int a = 10;
    int* p = &a;//明确地初始化，确定指向
    int* p2 = NULL;//不知道一个指针当前应该指向哪里时，可以初始化为NULL
    return 0;
}

#define N_VALUES 5
float values[N_VALUES];
float* vp;
for(vp = &values[0]; vp < &values[N_VALUES];)
{
    *vp++ = 0;
}

int main()
{
    int arr[10] = {1,2,3,4,5,6,7,8,9,0};
    int* p = &arr[9];
    printf("%p\n",p);
    printf("%p\n",p-2);
    return 0;
}

int main()
{
	int arr[10] = { 1,2,3,4,5,6,7,8,9,0 };
	printf("%d\n", &arr[9] - &arr[0]);
	printf("%d\n", &arr[0] - &arr[9]);
	return 0;
}

int main()
{
    int arr[10] = {1,2,3,4,5,6,7,8,9,0};
    char ch[5] = {0};
    printf("%d\n",&arr[9] - &ch[0]);//err
    return 0;
}

int my_strlen(char* s)
{
	int count = 0;
	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;
}

#define N_VALUES 5
float values[N_VALUES];
float *vp;
for(vp = &values[N_VALUES]; vp > &values[0];)
{
    *--vp = 0;
}

for(vp = &values[N_VALUES-1]; vp >= &values[0];vp--)
{
    *vp = 0;
}

int main()
{
	int arr[10] = { 0 };
	int sz = sizeof(arr);
	printf("%d\n", sz);
	return 0;
}

int main()
{
	int arr[10] = { 0 };
	int* p = arr;
	int i = 0;
	int sz = sizeof(arr) / sizeof(arr[0]);
	for (i = 0;i < sz;i++)
	{
		*(p + i) = i;
	}
	for (i = 0;i < sz;i++)
	{
		printf("%d ", *(p + i));
	}
	return 0;
}

int main()
{
    int a = 10;
    int* p = &a;
    int** pp = &p;//pp就是二级指针
    **pp = 20;
    printf("%d\n", a);//a = 20
    return 0;
}

int main()
{
	int arr[10];
	char ch[5];
	int* parr[5];
	char* pc[6];
	return 0;
}

int main()
{
	int a = 10;
	int b = 20;
	int c = 30;
	int* parr[3] = { &a,&b,&c };
	for (int i = 0;i < 3;i++)
	{
		printf("%d\n", *(parr[i]));
	}
	return 0;
}