I downloaded the chapter programs from this website and ran the Statistical Analysis of Array Data program, and instead of random numbers, I get exactly what is displayed in figure 6-2. It's supposed to generate random numbers, but I get the same results on every run. What's wrong with the line...

float randNum = (float) rand() / RAND_MAX; // From 0.0 to 1.0

rand() is not actually random, it is pseudo-random. You need to seed it first to create the "illusion" of randomness. If the seed doesn't change, the random numbers generated will be the same. A common technique is to seed with time()
srand(time(NULL));
Then use the program as written.
The value returned is what rand() will generate the pseudo-random numbers from. Unless the program is run at precisely the same time the numbers generated will change, since the seed will be different.
Google rand() and srand() for more info.
Bob