c++ help me to understand why there is no output [closed]

Here’s how it’s done with C++ I/O. There’s very little reason for using C I/O in a C++ program.

#include <iostream>
#include <string>

int main()
{
    std::string input;
    std::cin >> input; // take an input string
    long lval = stol(str); // convert to long
    std::cout << lval << '\n' // print the result
}

Now this stuff would be covered in the first chapter of any C++ book. A good book will greatly increase how quickly and how well you learn C++.