Newbie learning sorting algorithms and arrays

[peste19]

but i have the command here or am i missing something

ifstream input;
			
	input.open("data.txt");
	cout << "read how many entries" << endl;
	cin >> n;
	
	for (f=0;f<=n;f++);
	{
		input >> id[f];
		input >> grade[f];
	}