Question

say I have:

int lol;
cout << "enter a number(int): ";
cin >> lol
cout << lol;

If I type 5 then it’ll cout 5. If I type fd it couts some numbers.
How can I specify the value, like say I only want it an int?

Answer 1

If you type in fd it will output some numbers because those numbers are what lol happens to have in them before it gets assigned to. The cin >> lol doesn’t write to lol because it has no acceptable input to put in it, so it just leaves it alone and the value is whatever it was before the call. Then you output it (which is UB).

If you want to make sure that the user entered something acceptable, you can wrap the >> in an if:

if (!(cin >> lol)) {
    cout << "You entered some stupid input" << endl;
}

Also you might want to assign to lol before reading it in so that if the read fails, it still has some acceptable value (and is not UB to use):

int lol = -1; // -1 for example

If, for example, you want to loop until the user gives you some valid input, you can do

int lol = 0;

cout << "enter a number(int): ";

while (!(cin >> lol)) {
    cout << "You entered invalid input." << endl << "enter a number(int): ";
    cin.clear();
    cin.ignore(numeric_limits<streamsize>::max(), '\n');
}

// the above will loop until the user entered an integer
// and when this point is reached, lol will be the input number