Exercises and Challenges - Learning C# by Programming Games - page 404

3. Classes and interfaces
One of the following three combined declarations and assignments is correct.
Which one is that, and why are the other two not correct?
List< int >a= new IList< int >(); // version 1
IList< int >b= new List< int >(); // version 2
IList< int >c= new IList< int >(); // version 3
Describe a situation in which the correct version of the above lines of code has
an advantage over the also correct declaration and assignment:
List< int >d= new List< int >(); // version 4
4. List and foreach
Provided is the following class:
class Counter
{
int val = 0;
public Counter( int v)
{val=v;
}
public void Increment()
{
val++;
}
}
and the following instructions in a class that uses the Counter class:
List<Counter> list = new List<Counter>();
for ( int i=0; i<25; i++)
list.Add( new Counter(i));
(a) Write a method Increment , which gets an IList<Counter> object as a parameter
and which increments all the counters (using the Increment method in the
Counter class). Provide a version that uses the foreach instruction, as well as
a version that uses a for or a while instruction.
(b) Suppose that instead of passing a List<Counter> object, we would like to pass
an object of type OwnList<Counter> , where the OwnList class is our own ver-
sion of a list, which implements the IList interface. What do we need to
change in the Increment method we wrote in the previous question so that
we can use this method with our own list class?
5. Strings
The string class contains (among others) methods that have the following head-
ers: