Pointers to char

Hello. I have a problem with pointers to char.

First, I know that the following is valid:
char *a = "I am having a cup of coffee.";

However, the following is invalid, right? I must use strcpy, right?
In addition, can I leave the [] to be blank (i.e. not including any integer)?
char *a = new char[100];
a = "I am having a cup of coffee.";

Is the following acceptable? If no, why not?
char *a = "I am having a cup of coffee.";
cin >> a;

How about this?
char *a = new char[100];
cin >> a;

However, the following is invalid, right? I must use strcpy, right?
In addition, can I leave the [] to be blank (i.e. not including any integer)?
char *a = new char[100];
a = "I am having a cup of coffee.";

just put it in an array from the get go

char a[100] = "I am having a cup of coffee.";

when you use pointers, you have to do something special to write to the actual value of the variable being pointed to. for instance, this:

int b;
int *a = &b;
a = 0;

does not set b to 0, it sets the pointer a to point to memory location 0.
however, this:

int b;
int *a = &b;
*a = 0;

should set b to 0

someone who understands pointers better than me, feel free to correct me!