9.2.19

#include <iostream>
#include <string>
#include <fstream>
using namespace std;

int main() {
    ifstream in ("f1.txt");
    ofstream out("f2.txt");
    char c1 = '\0', c2 = '\0', seeker;
    cout << "Enter the seeker char: " << endl;
    cin >> seeker;
    while (in) {
        c1 = c2;
        in >> c2;
        if (c1 == seeker)
            out << c2;
    }
    in.close();
    out.close();
}