Answers to Chapter 18 Review Questions | C Primer Plus (5th Edition)

Chapter 18

1:	List three kinds of data abstractions where structs should be considered instead of classes.
A:	To represent fractions (with a numerator and a denominator To represent points on a map (2D) or points in space (3D) To represent a time span
2:	Mention the important similarities and differences between classes and structs.
A:	Similarities: structs and classes can both contain methods, properties, indexers, constructors, data members, operator methods, nested types; both can implement interfaces; and they both implicitly inherit from the `System.Object` class. Differences: Structs cannot contain destructors; their constructors work in a slightly different way. Structs form value types, whereas classes form reference types; structs don't support inheritance, and structs are stored more efficiently in memory.
3:	If `myStruct` is a value type, how is the following call possible if `WriteLine` only accepts reference types? Console.WriteLine("Details of myStruct" + myStruct);
A:	As part of the process of being passed as an argument to `WriteLine`, `myStruct` is boxed into a reference value, which then can be processed by `WriteLine`.
4:	Can a struct have an explicit default constructor?
A:	No.
5:	Why is boxing called boxing?
A:	One can imagine boxing as the process of putting a struct value into a box that is of a reference type.
6:	Suppose the struct `Fraction` contains the two public data members `numerator` and `denominator`. `Fraction` does not contain any explicitly defined constructors. You now write the following code: Fraction myFraction; myFraction.ToString(); Is the second line valid? Why or why not?
A:	No, the second line is not valid. `Fraction` does not contain any explicitly defined constructors, so the numerator and denominator values have not been initialized by the time `ToString` is called in the second line. This is invalid because no methods, properties, or indexers can be called for a struct value that contains uninitialized data members.

Answers to Chapter 18 Programming Exercises

Implement a struct called Fraction that contains two private data members of type int called numerator and denominator. Equip Fraction with the following elements:

A constructor that takes two arguments to initialize numerator and denominator
Properties to get and set numerator and denominator
A property called Value that simply returns the value of the fraction, which is calculated as (numerator / denominator)
Override the ToString method (implicitly inherited from System.Object) to return the following string: "Fraction value: xxx" where xxx represents the fraction value as a string.

Write suitable code to test the Fraction struct.

Exercise 1:

 using System; struct Fraction {     private int numerator;     private int denominator;     public Fraction(int initNumerator, int initDenominator)     {         numerator = initNumerator;         denominator = initDenominator;     }     public int Numerator     {         get         {             return numerator;         }         set         {             numerator = value;         }     }     public int Denominator     {         get         {             return denominator;         }         set         {             denominator = value;         }     }     public double Value     {         get         {             return (double)numerator / (double)denominator;         }     }     public override string ToString()     {         string returnString;         returnString = "Fraction value: " + Value;         return returnString;     } } class Tester {     public static void Main()     {         Fraction myFraction = new Fraction(1, 3);         Console.WriteLine(myFraction);     } }