指针系列一（指針的定義）

//指針的定義
    char a = 'f';
    int f = 123;
    char  *pa = &a;
    int *pb = &f;

    printf("a = %c\n", *pa);
    printf("f = %d\n", *pb);

    *pa = 'c';
    *pb = 1;

    printf(" now a = %c\n", *pa);
    printf(" now f = %d\n", *pb);

    printf("sizeof pa = %d\n", sizeof(pa));
    printf("sizeof pb = %d\n", sizeof(pb));

    printf("the addr of a is %p\n", pa);
    printf("the addr of b is %p\n", pb);

    //避免访问未初始化的指针，如定义  int *a;  
    //称之为 "野指针"