turning strings of unknown length into arrays

How do I read a string into an array without either fixing the length of the string or getting the user to enter the length first?

I thought this kind of thing might do it, but no joy:

char *H;
int i, n;

gets(H);
n = strlen(H);

for(i = 0; i < n; i++)
printf("%c", H[i]);

printf("\n");

I know I could do something like
char H[100];
but I wondered if there was another way?

You might try this:

char string[], c;
int i = 0;

while((c=getc(stdin)) != NULL)
{
string[i] = c;
i++;
}

You can't (directly)

This is what you do

Read (using fgets) input from the user into a fixed sized buffer (say 50 bytes).
Allocate a 50 byte block of memory, copy the user input to this buffer, and append this buffer to the end of a linked list of buffers.
Keep doing that until the user buffer contains the '\n' char (or some other end-of-input)

I guess this is stuff we haven't done yet. Linked lists seem to come up on this board all the time, so I should probably try and learn about them soon.
Thanks for your help guys...