Q:

Generating uniformly distributed random numbers within a range in C++

I know there are similar questions.
But mine has different settings.  

Have to use rand()
Have to use srand() to take a seed from user input
Only using standard library

I don't know if it's possible to get uniformly distributed random numbers, do I have to use the random library?

A:

The C++ standard mostly defers to the C standard when it comes to the heritage functions like rand() and srand().
Unfortunately, there is nothing in the C standard about rand() delivering uniform distribution. In fact, it states in a footnote (my emphasis):

There are no guarantees as to the quality of the random sequence produced and some implementations are known to produce sequences with distressingly non-random low-order bits. Applications with particular requirements should use a generator that is known to be sufficient for their needs.

If you want specific properties for your random numbers, you really should be using the C++ stuff in <random> (yes, I know you appear to have discounted that but you may have to make a trade-off: either use them or have no guarantee of a specific distribution).

