C++ function for picking from a list where each element has a distinct probability

Question

I have an array of structs and one of the fields in the struct is a float. I want to pick one of the structs where the probability of picking it is relative to the value of

Answer 1

float p = (rand() / static_cast<float>(RAND_MAX)) * total_probability;
s* current = &sArray[0];
while ( (p -= current->probability) > 0)
    ++current;
// `current` now points to your chosen target

Answer 2

Find out RAND_MAX as you say. Generate a random number up to RAND_MAX. Iterate through the array counting up the probabilities until you equal or exceed your generated random number. (With only 50 element performance shouldn't be an issue, otherwise store the sums of the probabilities once in another array and then do a bisection search into that for the random value.)