Generating big random numbers in C

[AwArEnEsS]

I want to generate big random numbers in C(not C++ please).By "big" I mean integers much bigger than srand(time(NULL)) and rand() functions' limit(32767).

I tried writing: (note:I am not able to see "code" tag button in this editor,so I am not using it)

//****

int randomnumber;
srand( time(NULL) );
randomnumber = (( rand() % 33 ) * ( rand() % 33 ) * ( rand() % 33) * ( rand() * 33) * (rand() % 33 )) + 1

//****

But I have doubts about it's randomness quality.Also there is another problem,the program can't know the maximum random number it should use before user input,so maximum random number may need to use much smaller maximum random number according to user input.

Is there a better algorithm to create quality big random numbers in C?