Output as currency in C++

Question

I have a simple C++ command line program where I am taking an input from the user then displaying it as a price, with a currency symbol, commas separating each set of 3 values, a decimal point, and two decimal places which will display even if they are zero.

Example of what I am trying to achieve:

100 => £100.00
101.1 => £101.10
100000 => £100,000.00

Here is my method so far:

void output_price() {
    int price;

    cout << "Enter a price" << endl;
    cin >> price;
    string num_with_commas = to_string(price);
    int insert_position = num_with_commas.length() - 3;
    while (insert_position > 0) {
        num_with_commas.insert(insert_position, ",");
        insert_position -= 3;
    }

    cout << "The Price is: £" << num_with_commas << endl;
}

This is partly working but doesn't show the decimal point/places.

1000 => £1000

If I change price to a float or double it gives me this:

1000 => £10,00.,000,000

I am trying to keep things simple and avoid creating a currency class, however not sure if this is possible in C++.

Any help appreciated.

There is never a need to create a class like currency, but it is a good idea and not that complicated that you should avoid it. — stefaanv, Oct 31 '15 at 17:25
Look up the `iomanip` header. More particularly into `std::setprecision`. — DeiDei, Oct 31 '15 at 17:25
You might fare better in your research if you abstract away the fact that this is currency, and simply search for how to render thousands separators and a fixed number of decimal places, in any arbitrary value. Though, since we're speaking currency, I recommend storing your values as integer pennies (or tenth-pennies), rather than going down the floating-point route. — Lightness Races in Orbit, Oct 31 '15 at 17:25
I do find it hard to believe your research turned up nothing useful for this. It's a very common requirement. — Lightness Races in Orbit, Oct 31 '15 at 17:27
`std::put_money` already exists. There's no need to reinvent it and do things like assume the user wants £ as the currency symbol. — chris, Oct 31 '15 at 17:32

score 1 · Accepted Answer · edited May 23 '17 at 10:27

The logical error is here:

int insert_position = num_with_commas.length() - 3;

The original value of num_with_commas could have any number of digits after the dot, including no dot at all; moreover, you have no control over it, because the format applied by std::to_string is fixed.

If you would like to continue using std::to_string, you need to make a few changes:

Locate the position of the dot '.' character.
If the dot is there, and the number of characters after it is less than 2, keep appending zeros "0" until dot '.' is the third character from the back
If the dot is there, and there are more than two characters after it, remove the tail of the string so that there are exactly two characters after the dot
If the dot is not there, append ".00" to string

The rest of your algorithm that inserts dots will work fine.

Output as currency in C++

1 Answers1