whereIt

#include <iostream>
#include <cstdlib>
#include <fstream>
#include <Windows.h>
using namespace std;

#define O_F_NAME "output.txt"

int main()
{
    char f_name[80], need;

    cout << "Enter the file: ";
    cin.get(f_name, 80);

    ifstream in(f_name, ios::in);
    if (!in) {
        cout << "Error in opening file.\n\n";
        system("pause");
        exit(1);
    }

    cout << "\nEnter symbol for find: ";
    cin >> need;

    ofstream out(O_F_NAME, ios::out);
    if (!out) {
        cout << "Error in creating output file.\n\n";
        system("pause");
        exit(2);
    }

    out << "Result of searching for \"" << need << "\":\n\n";

// main cycle

    int i = 0, eofv = iostream::traits_type::eof();
    int prev = eofv, cur = eofv;
    bool needExit = false;

    while (!needExit) {
        int prevprev = prev;
        prev = cur;
        cur = in.get();

        needExit = (cur == eofv);

        if (prev != need) continue;

        out << ++i << ") '";
        if (prevprev != eofv) out << (char)prevprev;
        out << (char)prev;
        if (cur != eofv) out << (char)cur;
        out << "'\n";
    }

    cout << "\nSuccess. Found " << i << " matches.\n\n"
        << "Results of searching \"" << need << "\" in \"" << f_name
        << "\" placed in \"" << O_F_NAME << "\".\n\n";

    out.close();
    in.close();
    system("pause");
    return 0;
}