You must be calling rnd more than once to get a list of numbers. It should be obvious that calling rnd before the main loop would only generate one random number. You are aware that you can store the output of rnd in a variable? I.E.
num = rnd(4)
If you want the random number generator to produce the same numbers every time, you can seed the RNG with
randomize n, n being any integer. If you seed the RNG like this, every time you run the program you will get the same sequence of random numbers. Most people assign the output of the cpu clock to randomize,
randomize timer(), because the clock is always changing it ensures the random numbers are different every time the program is executed.
Do oranges know what colour they are?