Random number array bounded by values in second array

Could someone please point me to a good explanation of how this might be accomplished?

For example, let's say I have an array a[j] initialized to the values {3, 4, 5}. I want to build a second array filled with random numbers bounded below by zero and above by the values in the first array. So b[i] would be initialized to a random number in the following ranges: {0-3, 0-4, 0-5}

What is a good way of achieving this in C++?