Number of iterations to cover all random numbers

I read the answers to the various questions on how to generate random numbers between 0 and 1.

float random = ((float) rand()) / (float) RAND_MAX;

Now I'm curious. Considering that the generator repeats the numbers (for a truly random number), how many iterations do you think makes it cover almost all possibilities. I code in 'C' and use the 'gcc' compiler. Thanks in advance.