Question

for example we have created file in c++ how to write content in this file and then output on screen?

Answer 1

Taken from here.

Writing:

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

int main () {
    ofstream myfile;
    myfile.open ("example.txt");
    myfile << "Writing this to a file.\n";
    myfile.close();
    return 0;
}

Reading:

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

int main () {
    string line;
    ifstream myfile("example.txt");
    while(getline(myfile,line)) {
        cout << line << endl;
    }
    myfile.close();
    return 0;
}

You should really use Google.