好奇怪，输出为空，不知道哪里出了问题

#include <iostream>
#include <cstring>
#include <cmath>
using namespace std;
int s[20];
int a, b,r;
bool check1(int x)
{
    if ((x >= 1000 && x <= 9999) || (x >= 100000 && x <= 999999))
        return 0;
    return 1;
}
bool check2(int x)
{
    int cnt = 1;
    while (x > 0)
    {
        s[cnt] = x % 10;
        x /= 10;
        cnt++;
    }
    for (int i = 1; i <= cnt; i++)
    {
        if (s[i] != s[cnt - 1])
            return 0;
        
    }
    return 1;
}
bool check3(int x)
{
    for (int i = 2; i <= sqrt(x); i++)
    {
        if (x % i == 0)
            return 0;
    }
    return 1;
}
int main()
{
    cin >> a >> b;
    if (a % 2 == 0)a++;
    r = min(9999999, b);
    for (int i = a; i <= r; i=i+2)
    {
        if (check1(i)==0)continue;
        if (check2(i)==0)continue;
        if (check3(i)==0)continue;
        printf("%d\n", i);
    }
    return 0;
}