（4）C语言基础，学习笔记(指针 )

&运算符，用于取一个对象的地址
*是一个间接寻址符，用于访问指针所指向的地址的值
int *ptr 定义一个指针
int b = *ptr 用于访问指针所指向的地址的值
& 与 * 是 一对互逆运算

//值传递，不会影响最终的结果
void swap(int x, int y) {
    printf("交换前：x = %d, y =%d\n", x, y);
    int tmp = x;
    x = y;
    y = tmp;
    printf("交换后：x = %d,y = %d\n", x, y);

}

// 指针传递，变量的地址
void swap1(int* x, int* y) {
    printf("交换前：x = %p, y =%p\n", x, y);
    printf("交换前：*x = %d, *y =%d\n", *x, *y);
    int tmp = *x;
    *x = *y;
    *y = tmp;
    printf("交换后：x = %p, y =%p\n", x, y);
    printf("交换后：*x = %d, *y =%d\n", *x, *y);
}



int main() {

    int a = 2 , b =3;
    printf("交换前：a = %d, b = %d\n", a, b);
    swap(a,b);
    printf("交换后：a = %d, b = %d\n", a, b);
    printf("=======================\n");

    a = 20 , b = 30;
    printf("交换前：a = %d, b = %d\n", a, b);
    printf("交换前：&a = %p, &b = %p\n", &a, &b);
    swap1(&a,&b);
    printf("交换后：a = %d, b = %d\n", a, b);
    printf("交换后：&a = %p, &b = %p\n", &a, &b);


    return 0;
}

交换前：a = 2, b = 3
交换前：x = 2, y =3
交换后：x = 3,y = 2
交换后：a = 2, b = 3
=======================
交换前：a = 20, b = 30
交换前：&a = 000000000022FE4C, &b = 000000000022FE48
交换前：x = 000000000022FE4C, y =000000000022FE48
交换前：*x = 20, *y =30
交换后：x = 000000000022FE4C, y =000000000022FE48
交换后：*x = 30, *y =20
交换后：a = 30, b = 20
交换后：&a = 000000000022FE4C, &b = 000000000022FE48