Append digit to an int without converting to string?

Question

Is there a safe way of adding a digit at the end of an integer without converting it to a string and without using stringstreams ?

I tried to google the answer for this and most solutions suggested converting it to a string and using stringstreams but I would like to keep it as an integer to ensure data integrity and to avoid converting types.
I also read a solution which suggested to multiply the int by 10 and then adding the digit, however this might cause an integer overflow.
Is this safe to do or is there a better method for doing this? And if I do this multiply by 10 and add the digits solution, what precautions should I take?

Answer 1

Your best bet is the multiplication by 10 and addition of the value. You could do a naive check like so:

assert(digit >= 0 && digit < 10);
newValue = (oldValue * 10) + digit;
if (newValue < oldValue)
{
    // overflow
}

Answer 2

To prevent overflow:

if ((0 <= value) && (value <= ((MAX_INT - 9) / 10))) {
    return (value * 10) + digit;
}

In place of MAX_INT, you could use std::numeric_limits<typeof(value)>::max() or similar, to support types other than int.