A property as a parameter in a constructor?

[Ratte]

I am supposed to write a custom exception handling constructor. First, I need to write a read/write string property and then I write the constructor that somehow needs to accept this property as a parameter (among other things such as msg and inner exception).

Any ideas? This is how it is worded on a homework by the way.
Thanks.

[Ramy Mahrous]

class XYZ
{
string str;
public string Str
{
get { return str; }
set { str = value; }
}

public XYZ(string str)
{
this.str = str;
}
}