I just want to prevent the user from entering too large a value for my integer variable "max". Even a max == 300 triggers the warning. When I removed these warning statements, I could do well with max == 300 or larger. Could you please help? Thanks a lot!

Code:

// Exercise 12 - Chapter 4
// Find all prime numbers between 1 - max,
// where, max is given by the user
// Primes found using the simpliest method
/*
Given n, keep dividing n by 2, 3, ..., (n-1). If divisible by any of these,
then it's not a prime. Otherwise, it's a prime. By definition, 1 is not
a prime, and 2 is the only even prime.
*/
#include "std_lib_facilities.h"
#include <cmath>
bool is_prime(int);
int main()
{
cout << "Enter a terminal number to which to find all";
cout << " prime numbers from 1: ";
int max;
cin >> max;
**if(max > sizeof(max)) {
cout << "Number exceeding defined ranged!\n";
}**
while (true) {
cout << "Do you want to try again (Y/N): ";
string choice;
cin >> choice;
if (choice == "Y" || choice == "Yes" || choice == "yes" || choice == "y") {
cout << "Enter a terminal number to which to find all";
cout << " prime numbers from 1: ";
cin >> max;
break;
}
else if (choice == "N" || choice == "No" || choice == "no" || choice == "n") {
return 0;
}
}
vector <int> myprimes;
for (int i = 1; i <= max; ++i) {
if (is_prime(i)) {
myprimes.push_back(i);
}
}
for (unsigned i = 0; i < myprimes.size(); ++i)
cout << myprimes[i] << endl;
}
bool is_prime(int x)
{
bool found;
if (x < 2)
found = false;
if (x == 2)
found = true;
for (int i = 2; i < x; ++i) {
if ((x % i) == 0) {
found = false;
break;
}
else
found = true;
}
return found;
}