Why does C scanf only accept char a[n]?

#include <stdio.h>
int main(void)
{
    char *name;
    scanf("%s", name);
    printf("You've entered %s\n", name);

    return 0;
}

Look at the above code.

The book says it may or may not be compiled.

It can be compiled on my Linux. But it runs and I type hello, it is not right.

hello
You've entered (null)

I know name is an uninitialized pointer why may point to anything.

So the proper way to correct this is char name[81];

Now I made some change.

I initialize name at the very beginning, like this:

#include <stdio.h>
int main(void)
{
    char *name = "aaa";
    scanf("%s", name);
    printf("You've entered %s\n", name);

    return 0;
}

It can also be compiled. But when I type hello, I get this:

[Tom@localhost ~]$ ./a.out 
hello 
Segmentation fault (core dumped)

Now that name has been initialized which in my understanding should be given an specific address.

Why it still fails to work ?


Here