How to calculate the rand() function?

Question

C++ / C#

Initially, I set the boundaries of the segment. Then it must be written to a function.
For example, for the interval [-5., 5.] the function will look like this:

double random()										
{
  return (double) (-5.0) + (double)rand() / RAND_MAX * 10.0 ; // a = -5; b = 10
}

But I don’t understand how to make it so that I set the boundaries of the interval myself and everything is calculated in the function itself. Help me please.

Answer 1

inline int getRandomNumber(int start, int end) {
  return start + rand() % (end - start);
}

valid for getRandomNumber(10, 20);
rand() generates a number up to RAND_MAX,
% (end - start) "cuts off" (the remainder of the division) to 10, i.e. 555 % 10 = 5
start + shifts by 10 But it's better not to use rand
, but to use modern solutions https://stackoverflow.com/a/7560564/7458932
a whole separate header with a bunch of other generators
and for double https://stackoverflow.com/a/9324796/7458932

Answer 2

double random(int a, int b)										
{
  return (double) a + (double)rand() / RAND_MAX * (b-a) ; 
}

Yes, just like you. Only the numbers a and b were added to the function parameters. The length of the range is calculated as the difference between the end and the beginning.
Usage example:
PS if necessary, a, b can be made double