Умножение и деление

size = static_cast<size_t>((end - begin) / step) + 1;

last = min + step * (size - 1);

size = static_cast<size_t>((end - begin) / step + 1e-8) + 1;

size = (size_t)((end - begin) / step) + 1;

#include <iostream>
using namespace std;
 
int main(void)
{
    double begin = 1.0, end = 3.0, step = 1.0;
    int size = (end - begin) / step + 1.0;
    cout << size;
    return 0;
}

#include <iostream>
using namespace std;
 
int main(void)
{
    double begin = 1e-4, end = 1.0, step = 5.0e-6;
    int size = (end - begin) / step + 1.0;
    cout << "int size = " << size;
    double x = (1.0-1.0/10000.0) / (5.0 / 1000000.0) + 1.0;
    cout << "\ndoble size = " << x;
    return 0;
}

#include <iostream>
using namespace std;
 
int main(void)
{
    double begin = 1e-4, end = 1.0, step = 5.0e-6;
    double x = (end - begin) / step + 1.0;
    int size = x;
    cout << "int size = " << size;
    cout << "\ndouble size = " << x;
    return 0;
}

int main(void)
{
    int i = 0;
    while (++i != 320)
    {
        double begin = rand() * 1.0 / rand(), end = begin + rand() * 1.0 / rand(), step = (end - begin) / rand();
        double x = (end - begin) / step + 1.0;
        int size = x;
        if (size != x)
        {
            cout << begin << ' ' << end << ' ' << step << ' ' << x << ' ' << size << endl;
        }
    }
}

int main(void)
{
    int i = 0;
    int right(0);
    int wrong(0);
    while (++i != 320)
    {
        double begin = rand() * 1.0 / rand(), end = begin + rand() * 1.0 / rand(), step = (end - begin) / rand();
        double x = (end - begin) / step + 1.0;
        int size = x;
        if (size != x)
        {
            cout << begin << ' ' << end << ' ' << step << ' ' << x << ' ' << size;
            ++wrong;
        }
        else
        {
            cout << "all right";
            ++right;
        }
    }
    cout << right << ' ' << wrong << endl;
}

if (size != static_cast<int>(x) )