Answers to Chapter 6 Review Questions | C Primer Plus (5th Edition)

Chapter 6

1:	Why are there two ways to categorize the types in C#?
A:	The distinction "Simple types versus derived types" is used for historical reasons and because it is convenient, but it is strictly speaking not correct. In contrast "Value types versus reference types" is correct but perhaps less intuitive.
2:	Why does C# have other simple types than `int`?
A:	Different types are needed to represent different kinds of data.
3:	Which kind of attributes distinguish the different types from each other?
A:	The kind of data the type can represent, the memory use, the kind of operations in which it will take part, and in case it can hold simple numbers: the range and precision.
4:	What does it mean to be a strongly typed language like C#?
A:	A strongly typed language attempts to prohibit types from being involved in processes in which they are not meant to participate.
5:	Is it possible to assign a value of type `int` to a variable of type `short,` without an explicit conversion? Why or why not?
A:	No, because assigning a value of type `int` to a variable of type `short` potentially results in loss of magnitude. Any assignment with the potential risk of data loss (magnitude or precision) requires an explicit conversion.
6:	How do you specify a literal to be of type `float`?
A:	By appending an `f` (or `F`) to the number. Thus, `6.89f` is a literal of type `float`.
7:	Write a line of code that declares a `private` instance variable called distance, which is of type `float` and is initialized to `100.5`.
A:	`private float distance = 100.5f;.`
8:	A variable of type `byte` is holding the value `255`. The program now attempts to increment the value by one. What happens: If the compiler switch is set to `unchecked`? If it is set to `checked?`
A:	If the compiler switch is set to `unchecked`, the variable overflows to make its value equal to 0. If it is set to `checked` a runtime error occurs.
9:	Which simple type would you use for a variable storing an arbitrary person's weight (in pounds)? (1 pound is approximately 0.45 kilos)?
A:	The simple type `float`.
10:	Which simple type would you use for storing account balances that would be involved in interest rate calculations requiring extremely high precision?
A:	The simple type `decimal`.
11:	Suppose `myNumber` and `yourNumber` are both of type `float`. Write a statement that adds these values together as `int`s and assigns them to an `int` variable.
A:	`myIntValue = (int)myNumber + (int)yourNumber;.`
12:	If `number1` and `number2` are of type `int` and `text1` is of type `string`, what is the type of the following expression? number1 + text1 + number2
A:	The expression is of type `string.`
13:	Is the following expression `true` or `false` when evaluated in C# and why? `((10 * 0.2f) == 2.0)`
A:	`0.2f` is not exactly 0.2. This inaccuracy is exposed when `(10 * 0.2f)` is compared to a value of type `double`, such as 2.0, resulting in the expression to be `false`.
14:	When should you use constants in your source code? What are their advantages?
A:	Use constants when your source code contains values that are constant throughout the lifetime of the program. The advantages of using constants are It is easier to understand the meaning of a name like Pi instead of a literal like 3.14. The use of constants allow you to change a value in one place (where it is declared) rather than in every place it is used in the source code.
15:	Write a statement that prints 30000000.326m onscreen with this format: $30,000,000.33
A:	`Console.WriteLine(30000000.326m.ToString("C"));.`

Answers to Chapter 6 Programming Exercises

1:	Enable the clock to be adjusted by plus/minus 100 seconds by giving the commands `H` and `M`.
2:	A year on Blipos has 256 days. The first day of the year has number 0. The civilization is very old on Blipos; their current year is 4,294,967,296. Allow the Blipos clock to show the date on Blipos as ddd/y,yyy,yyy,yyy. Which types would you choose for ddd and yyyyyyyyyy?
3:	Allow the user to set and adjust the day and year of the Blipos clock so that it becomes possible to move forward and backward in time by one day and one year.
4:	The emperor's birthday is celebrated on the 100^th day of each year. Enable the Blipos clock to write "Happy birthday emperor!" onscreen whenever the date is shown to be the 100^th day of the year.
A:	The following source code provides answers to programming Exercises 1 4. The code parts related to a particular exercise have been marked with a comment, such as `// Ex.1` or `// Exercise 1`. using System; class BliposClock { private byte seconds; private short minutes; //Exercise 2 private byte days; private ulong years; public BliposClock() { seconds = 0; minutes = 0; // Exercise 2 days = 0; years = 0; } public void OneForward() { byte originalSeconds = seconds; short originalMinutes = minutes; //Ex. 2 byte originalDays = days; //Ex. 2 seconds++; if (originalSeconds > seconds) // Overflow of seconds variable minutes++; // Exercise 2 if (originalMinutes > minutes) // Overflow of minutes variable days++; if (originalDays > days) // Overflow of days variable years++; } public void OneBackward() { byte originalSeconds = seconds; short originalMinutes = minutes; //Ex. 2 byte originalDays = days; //Ex. 2 seconds--; if (originalSeconds < seconds) // Underflow of seconds variable minutes--; // Exercise 2 if (originalMinutes < minutes) // Underflow of minutes variable days--; if (originalDays < days) // Underflow of days variable years--; } public void FastForward() { byte originalSeconds = seconds; short originalMinutes = minutes; //Ex. 2 byte originalDays = days; //Ex. 2 seconds = (byte)(seconds + 50); if (originalSeconds > seconds) // Overflow of seconds variable minutes++; // Exercise 2 if (originalMinutes > minutes) // Overflow of minutes variable days++; if (originalDays > days) // Overflow of days variable years++; } public void FastBackward() { byte originalSeconds = seconds; short originalMinutes = minutes; //Ex. 2 byte originalDays = days; //Ex. 2 seconds = (byte)(seconds - 50); if (originalSeconds < seconds) // Underflow of seconds variable minutes--; // Exercise 2 if (originalMinutes < minutes) // Underflow of minutes variable days--; if (originalDays < days) // Underflow of days variable years--; } // Exercise 1 public void HundredForward() { byte originalSeconds = seconds; short originalMinutes = minutes; //Ex. 2 byte originalDays = days; //Ex. 2 seconds = (byte)(seconds + 100); if (originalSeconds > seconds) // Overflow of seconds variable minutes++; // Exercise 2 if (originalMinutes > minutes) // Overflow of minutes variable days++; if (originalDays > days) // Overflow of days variable years++; } // Exercise 1 public void HundredBackward() { byte originalSeconds = seconds; short originalMinutes = minutes; //Ex. 2 byte originalDays = days; //Ex. 2 seconds = (byte)(seconds - 100); if (originalSeconds < seconds) // Underflow of seconds variable minutes--; // Exercise 2 if (originalMinutes < minutes) // Underflow of minutes variable days--; if (originalDays < days) // Underflow of days variable years--; } // Exercise 3 public void AddOneDay() { byte originalDays = days; days++; if (originalDays > days) // Overflow of days variable years++; } // Exercise 3 public void DeductOneDay() { byte originalDays = days; days--; if (originalDays < days) // Underflow of days variable years--; } // Exercise 3 public void AddOneYear() { years++; } // Exercise 3 public void DeductOneYear() { years--; } public void SetSeconds(byte sec) { seconds = sec; } public void SetMinutes(short min) { minutes = min; } // Exercise 2 public void SetDays(byte newDays) { days = newDays; } // Exercise 2 public void SetYears(ulong newYears) { years = newYears; } public void ShowTime() { Console.WriteLine("Sec: " + seconds + " Min: " + minutes); // Exercise 2 Console.WriteLine("Day/year: " + days + "/" + years); // Exercise 4 if (days == 100) Console.WriteLine("Happy Birthday Emperor!"); } } class RunBliposClock { public static void Main() { string command; Console.WriteLine("Welcome to the Blipos Clock. " + "256 seconds per minute " + "65536 minutes per day"); BliposClock myClock = new BliposClock(); Console.WriteLine("Please set the clock"); Console.Write("Enter Seconds: "); myClock.SetSeconds(Convert.ToByte(Console.ReadLine())); Console.Write("Enter Minutes: "); myClock.SetMinutes(Convert.ToInt16(Console.ReadLine())); Console.Write("Enter Days: "); //Ex.2 myClock.SetDays(Convert.ToByte(Console.ReadLine())); //Ex.2 Console.Write("Enter Years: "); //Ex.2 myClock.SetYears(Convert.ToUInt64(Console.ReadLine())); //Ex.2 Console.WriteLine("Enter command: F) Forward B) Backward " + "A) Add fifty "); Console.WriteLine("D) Deduct fifty H) Add hundred " + //Ex.1 "M) Deduct hundred "); //Ex.1 Console.WriteLine("Q) Add one Day Y) Add one year " + //Ex.3 "U) Deduct one day\n W) Deduct one year T) Terminate"); //Ex.3 do { command = Console.ReadLine().ToUpper(); if (command == "F") myClock.OneForward(); if (command == "B") myClock.OneBackward(); if(command == "A") myClock.FastForward(); if(command == "D") myClock.FastBackward(); //Exercise 1 if(command == "H") myClock.HundredForward(); if(command == "M") myClock.HundredBackward(); //Exercise 3 if(command == "Q") myClock.AddOneDay(); if(command == "Y") myClock.AddOneYear(); if(command == "U") myClock.DeductOneDay(); if(command == "W") myClock.DeductOneYear(); myClock.ShowTime(); } while (command != "T"); Console.WriteLine("Thank you for using the Blipos Clock"); } }
5:	Write a program containing a method called `AverageAge` that calculates the average of three ages provided to it as arguments. Enable the user to enter three ages (as whole numbers) and use `AverageAge` to calculate the average age and print the result with a precision of three decimals. Which return type would you use for `AverageAge`? How can you format the output?
A:	The following source code constitutes the answer to Exercise 5. using System; class AgeCalculator { public double AverageAge(byte age1, byte age2, byte age3) { double average; average = (double)(age1 + age2 + age3) / 3; return average; } } class Tester { public static void Main() { byte ageA; byte ageB; byte ageC; AgeCalculator myCalculator = new AgeCalculator(); Console.Write("Enter age 1: "); ageA = Convert.ToByte(Console.ReadLine()); Console.Write("Enter age 2: "); ageB = Convert.ToByte(Console.ReadLine()); Console.Write("Enter age 3: "); ageC = Convert.ToByte(Console.ReadLine()); Console.WriteLine("Average age: " + myCalculator.AverageAge(ageA, ageB, ageC).ToString("N3")); } }