指针

    int  a = 5;
    printf("%d \n", a);
    printf("p = %p\n", &a);
    //打印a的地址
    //%p - 16进制格式打印  -- 通常用来对应地址格式
    //定义一个指针类型变量
    //NULL代表空的意思（即指针类型的0）
    int *p = NULL;
    //指针变量在内存中也有空间，空间用来存所指向的变量的地址
    p = &a;
    p = &a;
    printf("p = %p\n",p);

    通过指针访问内存单元存储的具体数值
    指针部分两重要的运算符
    & - 取址运算符 ，获取变量所在的地址
    * - 取值运算符 ，获取地址中存的具体数值
    printf("%d \n", *p);
    printf("%d \n", *(&a));



    有两个整形变量 a = 3，b = 5，定义两个指针 p ，q ，通过指针完成对a，b值的交换，
    提示：空瓶定义成普通类型变量：如  int temp = 0；
    int a = 3;
    int b = 5;
    int temp = 0;
    int *p = &a;
    int *q = &b;
    printf("a = %d   b = %d \n", *p, *q);
    printf("*p = %d   *q = %d\n\n", *p, *q);

    temp = *p;
    *p = *q;
    *q = temp;

    printf("a = %d   b = %d\n", a, b);
    printf("*p = %d   *q = %d\n", *p, *q);

    int* cc = &a;
    printf("%d \n",*cc);

    指针运算  只关心加减   p++   p--




    加减乘除
    int a = 4;
    int b = 3;
    int *p = &a;
    int *q = &b;

    //加
    int addA = add (p, q);
    printf("%d \n", addA);
    //减
    int subA = sub (p, q);
    printf("%d \n", subA);

    //乘
    int mulA = mul( p, q);
    printf("%d \n", mulA);

    //除
    int diviA = divi (p, q);
    printf("%d \n", diviA);


    int a[4] = {1, 2, 3, 4};
    int *p = NULL;
    //指向数组首地址
    p = a;
    //访问数组的第二个元素
    p++;
    printf("%d ", *p);

    p = &a[1];
     printf("%d ", *p);

    p = a;
    printf("%d ", a[1]);
    printf("%d ", *(a + 1));
    printf("%d ", *(p + 1));
    printf("%d ", p[1]);

    for (int i = 0; i < 4; i++) {
        printf("%d ", *(p + i));
    }
    printf("\n");

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