Working reading string to Numbers, custom stoi function

#include <iostream>
#include <string>
#include <string.h>
#include <cstdlib>
#include <sstream>      // std::stringstream

using namespace std;



string input = " ";


long sstoi(const char *s) // custom stoi function
{
    long i;
    i = 0;
    while(*s >= '0' && *s <= '9')
    {
        i = i * 10 + (*s - '0');
        s++;
    }
    return i;
}
int main() {

    int k = 0;
    cin >> k;
    string newString[k] = {};
    long long numbers[k] = {};
    int output[k] = {};
    cin.sync();

    for(int i =0; i<k; i++)
    {

        getline(cin, input);
        newString[i] = input.erase(input.size() - 1);
        //numbers [i] = atoi(newString.c_str()); // S tova ne raboti
         numbers[i] = sstoi (input.c_str());



    }

    for( int i =0; i<k; i++)
    {

        cout << numbers[i] << endl;

    }


}