rand() % N will give you a value in the range of 0 to N-1, inclusive. To get a number between any arbitrary minimum and maximum, take the make N the difference of the maximum and minimum, then shift the range by adding the minimum:

#include <stdio.h>
#include <stdlib.h>
#include <time.h>

#define RMIN 10
#define RMAX 30

int main(void)
{
    srand((unsigned)time(NULL));
    
    for (int x = 0; x < 10; x++)
    {
        printf("%d\n", rand() % (RMAX - RMIN) + RMIN);
    }
    
    return 0;
}

srand() is used to reseed the generator each time the program is run. Otherwise you'll get the same sequence because the default seed is always 1.

If this is really C++, you have more options with the various new random engines and distribution classes. I default to the Mersenne Twister and uniform int distribution instead of C's rand() because it's a much better engine and I don't have to do any mental math to make sure the range formula is right.

#include <functional>
#include <iostream>
#include <random>
#include <ctime>

namespace
{
    const int RMIN = 10;
    const int RMAX = 30;
}

int main()
{
    using namespace std;
    
    auto rgen = bind(
        uniform_int_distribution<int>(RMIN, RMAX - 1),
        mt19937(time(nullptr))
    );
    
    for (int x = 0; x < 10; x++)
    {
        cout << rgen() << '\n';
    }
}