How many numbers have k

// У скольких целых чисел, лежащих в диапазоне от 1 до n, есть цифра k?
#include <iostream>
using namespace std;
int main()
{
    int n, k, counter = 0;
    cout << "Enter number from 1 to 9999: ";
    cin >> n;
    cout << "Enter searching number (from 1 to 9): ";
    cin >> k;
    if (n > 9999 || n < 1) {
        cout << "Entered number is invalid\n";
        system("pause");
        main();
    }
    if (k<=0||k>9) {
        cout << "Entered searching number is invalid\n";
        system("pause");
        main();
    }
    for (int i = 1; i <= n; i++) {
        if (i == k) {
            counter++;
            continue;
        }
        if (i > 10 && i < 100) {
            if (i / 10 == k) {
                counter++;
                continue;
            }
            if (i % 10 == k) {
                counter++;
                continue;
            }
        }
        if (i > 100 && i<1000) {
            if (i / 100 == k) {
                counter++;
                continue;
            }
            if ((i % 100) / 10 == k) {
                counter++;
                continue;
            }
            if ((i % 100) % 10 == k) {
                counter++;
                continue;
            }
        }
        if (i > 1000) {
            if (i / 1000 == k) {
                counter++;
                continue;
            }
            if ((i % 1000) / 100 == k) {
                counter++;
                continue;
            }
            if (((i % 1000) % 100) / 10 == k) {
                counter++;
                continue;
            }
            if (((i % 1000) % 100) % 10 == k) {
                counter++;
                continue;
            }
        }
    }
    cout << "There are " << counter << " numbers between 1 and " << n << " that have " << k << endl;
    system("pause");
    return 0;
}