c++: Input minutes and seconds separated with ':'

Question

So, I'm a beginner at c++. I have an assignment where I have to use a struct for time length and use operator overloading to input a time length (minutes and seconds) separated with ':'. So my question: How can I let the compiler know that ':' is an enter (so it registers the minutes)? So if I fill in for example 2:40, It should be registered like this: length.minutes = 2 and length.seconds = 40

struct Length
{
    int minutes;            // #minutes (0..)
    int seconds;            // #seconds (0..59)
};

Length l1 = {42,42}, l2 = {0,0}, l3 = {3,21}, l4 = {3,14};

istream& operator>> (istream& in, Length& length)
{// Precondition:
    assert (true) ;
/*  Postcondition:
    the value of length has been read from in: first minutes, then ':', then seconds
*/
    in >> length.minutes >> ':' >> length.seconds;
}