Exercises

https://csci-1301.github.io/about#authors

April 5, 2024 (12:47:56 PM)

Homework #1

Part I — Questions

List five pieces of software, and three hardware components of a computer.
List four programming languages.
What is a GUI?
What is a CLI?
What, if any, is the difference between a compiler and an assembler?
Is machine code (or the machine language program) is made of circuits, binary numbers, classes, or compilers?
Give a specific characteristic of C# compared to other programming languages.
What happens when the source code you are giving to the compiler has a syntax error?
Is the C# compiler case-sensitive?
Suppose I replace every empty space in your source code with two empty spaces. Will your program still compile? Why, or why not?
Give three keywords.
Write a statement that would display, “Hi Mom!” (without the quotes) followed by a new line on the screen, once inserted in a proper method, compiled, and executed.
Write a statement that would display, “Hello!” (without the quotes) followed by a new line on the screen, once inserted in a proper method, compiled, and executed.
What is the limitation, if any, to the number of methods you can have per class? Why is the method called Main special?
What is the difference between a “rule” and a “convention” in programming language?
What is a namespace?
In a C# program, can comments start with \\ (double backslash) or with // (double (forward) slash)? Do they have to end with a ; (semicolon)?
Which of the following, if any, are keywords? Welcome1 public apples int "I’m a string"
Which of the following are programmer-defined names (or identifiers)? BankAccount class apples int itemPerCapita statement
Why are variables called “variables”?
What is string interpolation?
What is the difference, if any, between 12, and "12"?
What is the difference, if any, between the WriteLine and Write methods?
Write a statement that would display the following on the screen: Hi Mom!↵ How are you doing?
Assume we have a variable whose name is myVariable, type is string, and value is "My message". What would be displayed on the screen by the following statement? Console.WriteLine($"Here is my variable: {myVariable}");
Assume we have a variable whose name is level, whose type is string, and whose value is "Easy". What would be displayed at the screen by the following statement? Console.WriteLine($"You set the difficulty to {level}.");
Which of the following are correct identifier names? $myHome3 class my%variable ANewHope _train _ThisIsAVariable statement Is the name myVariable the same as myvariable? If not, why?
Which of the following are correct identifier names? myClass _Exo_1 Lab3-Exo1 My.Lab.Variable using Lab3_Part1
Which of the following are keywords? myClass static Lab3-Exo1 “Hello World” using Lab3_Part1
Which of the following are correct identifier names? 12_Dec_2019 Lab3-Exo1 MyClass2 My.Lab.Variable string My_Var
Which one(s) of the following, if any, is a correct assignment (assuming that variable, x and apples have been declared as int variables)? 5 => variable; x=5; apples= 23 x <= 23; variable =1,890;
Write a statement that assigns the value 23 to a variable myAge of type int. You do not need to re-declare that variable.
Cross out the wrong answer in the following sentences, [ ~~like this (incorrect)~~ | like this (correct) ]:
- “If the code does not obey the [ rules | conventions ] of C#, then the compiler will complain.”
- “Every statement needs to end with [ a forward slash / | a semi-colon ; ].”
- “C# is a [ object-oriented | functional ] programming language.”
- “A class is made up of [ a body and a header | multiple using statements ].”
- “An identifier can contain [ only lower-case letters | letters and digits ].”

Part II – Problems

There are 4 errors in the following code that will prevent it from compiling. Can you spot them all?

// My first attempt.
using System
class Wel
{
    static void Main();
    {
        ConsoleWriteLine("Welcome \n to the lab!");
    }

Homework #2

Part I — Questions

In C#, what is the “escape character”? Why is it useful?
Write a statement that initializes a variable named myHeightInMeters to your height in meters. What should be the datatype of myHeightInMeters?
Suppose you replace every * in your program with the ! symbol. Are you completely sure that your program would still compile? Why or why not?
Give the values of a and b after the following four instructions have been executed. int a, b; a = 2; b = a * 2 + 1; a -= 1;
Give the values of a and b after the following four instructions have been executed. int a, b; a = 4; b = a * 3 + 1; a /= 2;
Give the values of c and d after the following four instructions have been executed. int c = 3, d; d = 2 + c; c = d * 2; d += 2;
Is there an error in the following code? Explain the error or give the value of b after the second statement is executed. float a = 3.7f; int b = (int)a;
Is there an error in the following code? Explain the error or give the value of b after the second statement is executed. decimal a = 1.6M; int b = (int)a + a;
There is an error in the following code, at the second line. Explain the error, and how you could fix this second line using a cast operator, without changing the datatype of the b variable. decimal a = 2.5M; int b = a / 2;
If one of the operator’s operands is of type float and the other is of type int, what will be the type of the result of the operation?
What is the return type of the operation 12.4 * 3?
Write an explicit conversion from a double variable myDoubleVar to an int variable called myIntVar. You do not need to re-declare those variables. Assuming myDoubleVar’s value is 5.89, what value would be stored in myIntVar?
Write a statement that performs an implicit conversion between two different numeric datatypes.
Assuming that myLastName and myFirstName are two string variables that have been initialized, write a statement that concatenates them with a space and a comma in-between, and assign the resulting string to a variable named fullName. For instance, if the value of myLastName is "Holbertonand", and the value of myFirstName is "Betty", then the value of fullName after your operation should be "Holbertonand, Betty".
In C#, what is the name of the method used to read input from the user?
What is wrong with the following code? Will the error(s) appear at compilation time or at execution time? int age; Console.WriteLine("Please enter your age:"); age = Console.ReadLine();
Will those statements, if placed in a proper Main method, compile? Could this program crash at execution time? Justify your answer. int myAge; Console.WriteLine("Please enter your age:"); myAge = int.Parse(Console.ReadLine());
Write a series of statements that: a) Declare an int variable named userAge, b) Display on the screen a message asking the user to enter his or her age, c) Read the value entered by the user and store it in the userAge variable. You can add statement(s) performing intermediate steps if you want.
Write a series of statements that: a) Declare an string variable named favoriteColor; b) Display on the screen a message asking the user to enter his or her favorite color; c) Read the value entered by the user and store it in the favoriteColor variable. You can combine some of the statement(s) if you want, but do not display at the screen any information that was not explicitely asked.

Part II – Problems

The following three exercises do not require a computer. Make sure you feel ready before starting them, try to do them with limited time and without notes, and, if you want, check your answer using your IDE.

This problem restates the content of the Order of Operations section of the lecture notes and ask you to answer various problems.

There are 5 different arithmetic operations available in C#:

Operation	Arithmetic Operator	Algebraic Expression	Expression
Addition	`+`	x + 7	`myVar + 7`
Subtraction	`-`	x − 7	`myVar - 7`
Multiplication	`*`	x × 7	`myVar * 7`
Division	`/`	x/7, or x ÷ 7	`myVar / 7`
Remainder (a.k.a. modulo)	`%`	x mod 7	`myVar % 7`

Computing operations involving one of them is straightforward:

Operation	Result
`3 + 4`	`7`
`3 - 4`	`-1`
`3 * 4`	`12`
`6 / 2`	`3`
`6 % 4`	`2`

But things can get complicated when multiple operators are used, but no parenthesis are indicated. For instance, should

7 / 2 - 4 * 8 % 3

be read as

(7 ÷ 2) − ((4 × 8) mod 3)	= 3.5 − (32 mod 3)
	= 3.5 − 2
	= 1.5

or as

(7 ÷ (2 − 4)) × (8 mod 3)	= (7 ÷ (−2)) × 2
	= (−3.5) × 2
	= −7

Certainly, the result is not the same and there are other possibile ways this calculation may be performed!

Actually, C# uses the following three rules:

*, /, and %, called the “multiplicative operations,” are always evaluated before + and -, called the “additive operations.” So that, for instance,
```
2 - 4 * 8
```
will be evaluated as 2 − (4 * 8) = −30.
If there are multiple operations of the same type, they are evaluated from left to right. For instance,
```
4 / 2 * 8
```
will be evaluated as (4 ÷ 2) × 8 = 16 and
```
4 - 2 + 8
```
will be evaluated as (4 − 2) + 8 = 10.
Parenthesis can be used to force a particular order of evaluation, so that 2 * (3 + 4) will be evaluated as 2 × (3 + 4) = 2 × 7 = 14, not as (2 × 3) + 4 = 6 + 4 = 10 as it would without the parenthesis.

Answer the following:

Which of the following operation(s) compute the arithmetic expression (x × (3 mod 5)) − (y × 7)?
1. x * 3 % 5 - y * 7
2. x * (3 % 5) - y * 7
3. (x * 3) % 5 - y * 7
4. x * 3 % (5 - y * 7)
5. (x * 3 % 5) - (y * 7)
6. (x * ((3 % 5) - (y * 7))
State the order of evaluation of the operators in each of the following operations, and compute the resulting value:
1. 8 - 39 * 1 / 12 + 5
2. 12 + -23 / 12 % 3
3. 90 * 23 / 34 - 12 - 13
4. 12 % 83 - 2 * 3
(Optional) Check your answers using your IDE. You can use a statement of the form:
```
Console.WriteLine($"8 - 39 * 1 / 12 + 5 is {8 - 39 * 1 / 12 + 5}");
```

Write down, on a piece of paper, a fully compilable program that initializes an int variable named persons with the value 5, an int variable named bottles with the value 3, and a double variable named literPerBottle with the value 1.5. What should be the type of the literPerPerson variable to be able to be assigned the number of liters every person is going to get, if split equitably? Write the correct initialization of that variable and a statement that displays its value.

Place a delimited comment with a your name and the time at which you wrote the program at the top of the program.
Write down, on a piece of paper, a program that:
1. Declares a string variable named userName.
2. Displays on the screen “Please enter your name, followed by enter:”.
3. Reads a string value from the keyboard and assigns the value to the userName variable.
4. Declares an int variable named number.
5. Displays on the screen “Please enter your number:”.
6. Reads an int value from the keyboard and assigns the value to the number variable.
7. Declares a string variable named id and initializes it with the string referenced by the userName variable, followed by the number entered by the user (you can concatenate a string and an int using the + sign).
8. Displays on the screen, “Your id is” and the content of the id variable.
Here is an example of execution, where the user input is underlined, and hitting “enter” is represented by ↵:

{text} Please enter your name, followed by enter. J͟a͟y͟l͟a͟h͟↵͟ Please enter your area code, followed by enter. 4͟9͟3͟9͟1͟↵͟ Your id is Jaylah49391 Press any key to continue . . .

Homework #3

Part I – Questions

What is “an instance of a class”?
Fill in the blanks: “A class asserts that every objects created using it should have ͟ ͟ ͟ ͟ ͟ ͟ ͟ ͟ ͟ ͟ ͟ ͟ ͟ ͟ ͟ ͟ ͟ ͟ ͟ ͟ ͟ ͟ ͟ ͟ ͟ ͟ ͟ ͟ (i.e.,”data”) and ͟ ͟ ͟ ͟ ͟ ͟ ͟ ͟ ͟ ͟ ͟ ͟ ͟ ͟ ͟ ͟ ͟ ͟ ͟ ͟ ͟ ͟ ͟ ͟ ͟ ͟ ͟ ͟ (i.e., “operations”).”
Give two access modifiers.
What, if any, is the difference between a parameter and an argument?
Write a statement that creates a new object from the Rectangle class.
What is the purpose of the keyword new?
Do different objects from the same class share their instance variables?
Briefly explain the difference between a local variable and an instance variable.
Suppose we have a Circle class containing
```
public void SetRadius(double radiusArgument)
{
    radius = radiusArgument;
}
```
Write a statement that create a Circle object, and one statement that sets its radius to 3.5.
Indicate the order of evaluation of the operators in each of the following C# operations by adding parenthesis or developping the expression one step at a time, and compute the resulting value:
1. 3 * 4 - 2
2. 3 % 2 + 3
3. 2 - 3 + 3 * 2
4. 2 + 2 * 1 - 4
Write the complete implementation of a class that contains two attributes (with different data types), a setter for one attribute, a getter for the other attribute, a custom constructor, and a ToString method. You can re-use an example from a lecture or a lab, as long as it satisfies those conditions, or you can invent one. No need to write an application program.
What does the keyword return do?
Write a get method for an instance variable named total of type int.
Write a getter for an attribute of type string named myName.
Write a setter for an attribute of type int named myAge.
Assuming name is a string instance variable, there is problem with the following setter. Fix it.
```
public int SetName(string val){
    name = val;
}
```
Assume we have an instance of the Rectangle class named myRect and an instance of the Circle class named myCircle. Write statement(s) that will make the radius of myCircle equal to the width of myRect.
Briefly describe what a format specifier is. Write a statement that uses one.
Write a statement that uses a format specifier.
Write a method for the Rectangle class that divides the length and width of the calling object by a factor given as a parameter.
Draw the UML diagram of a class named “Student” with a single attribute, “name”, of type string, and two methods, SetName and GetName.
Write a ToString method for a Account class with two attributes, a string attribute called name and a decimal attribute called amount.
Consider the following UML diagram:

Circle

- radius : float

+ setRadius(radiusParam : float) : void

+ getRadius(): float

+ getArea(): float

What is the name of the class, what are the methods and attributes of the class?
What does it mean to say that instance variables have a default initial value? How is that different from the variables we have been manipulating in the Main method?
Is it possible to have more than one constructor defined for a class? If yes, how can C# know which one is called?
What is the name of a constructor method? What is the return type of a constructor?
Write a constructor for a Soda class with one string attribute called name.
Assume we have a Polygon class, that have only one attribute, an int called numberOfSides. Write a constructor for that class.
What is the “default” constructor? Do we always have the possibility of using it?
What is the return type of a ToString method? How many arguments does it usually take?
Consider the following partial class definition:
```
public class Book
{
    private string title;
    private string author;
    private string publisher;
    private int copiesSold;
}
```
1. Write a statement that would create a Book object.
2. Write a “getter” and a “setter” for the title attribute.
3. Write a constructor for the Book class taking at least one argument (you are free to decide which one(s)).
Consider the following partial class definition:
```
class DVD
{
    private string title;
    private decimal price;
}
```
1. Write a “setter” for the title attribute.
2. Write a constructor for the DVD class that takes two arguments.
3. Write a method called Discount that decreases the price attribute by 20.55%.
4. Write a (good, informative) ToString method for the class.
5. Write statements that ask the user to enter a price and then create a DVD object with a price attribute equal to the price the user entered. (The object’s title attribute can be anything you choose).
6. Draw the UML class diagram for the class you obtained by adding the above four methods to our original class definition.
Consider the following partial class definition:
```
class Book
{
    private string title;
    private decimal price;
}
```
1. Write a “getter” for the title attribute.
2. Write a constructor for the Book class that takes two arguments.
3. Write a method called AddTaxes that increases the price attribute by 6.35%.
4. Write a (good, informative) ToString method for that class.
5. Write statements that ask the user to enter a price and then create a Book object with a price attribute equal to the price the user entered. (The object’s title attribute can be anything you choose).
6. Draw the UML class diagram for the class you obtained by adding the above four methods to our original class definition.

Circle
- radius : float
+ setRadius(radiusParam : float) : void
+ getRadius(): float
+ getArea(): float

Assume that my Pet class contains one custom constructor:

public Pet(string nameP, char genderP){
    name = nameP;
    gender = genderP;
}

What is the problem with the following statement?

Pet myPet = new Pet('M', "Bob");

Why would one want to define a constructor for a class?

Part II – Problems

There is only one problem this time, and it is harder than what you’ll be asked to do during the exam. Being able to solve it is an excellent sign that you are ready.

You are going to design a class named Triangle. A triangle has three angles, but knowing the value of only two angles is sufficient to determine the value of the third, since they always add up to 180°. Hence, it is sufficient to have only two double attributes, angle1 and angle2. We want to define several methods:
- a no-arg constructor that sets the value of angle1 to 60.0 and the value of angle2 to 60.0,
- another constructor, that takes two arguments, and assigns to angle1 the value of the first argument, and assigns to angle2 the value of the second argument,
- getters for angle1 and angle2,
- a method that computes and returns the value of the third angle, that we name ComputeAngle3,
- a method that rotate the triangle: the value of the first angle should be replaced with the value of the second angle, and the value of the second angle should be replaced with the value of the third angle.
1. Write the UML diagram for the Triangle class.
2. Write the full, compilable implementation of the Triangle class.

Homework #4

Part I — Questions

What is sequential processing?
What is a decision structure?
Decide if the following boolean expressions will evaluate to true or false:
1. 3 > 2.0 && false
2. (4 != 3) || false
3. 'A' == 'b' && ! false
4. (! false) == (true || 4 == 3)
Decide if the following Boolean expressions will evaluate to true or false:
1. 3 > 2.0 || true
2. (4 != 3) && false
3. 'A' == 'b' || ! false
4. (! true) == (true || 4 != 3)
For each of the following Boolean expressions, decide if it will evaluate to true or false:
1. ('y' == 'Y') && true
2. 6 + 2 < 8 || 3 > 4
3. (true && 4 == 3) == false
4. 4 > 4 && !false
For each of the following Boolean expressions, decide if it will evaluate to true or false:
1. ('y' != 'Y') && true
2. 6 + 2 < 12 || 3 > 4
3. (true && 4 >= 3) == false
4. 13 <= 4 * 3 || !false
What relational operator is used to determine whenever two values are different?
How do you store the result of a Boolean expression?
Give three relational operators, and then two logical operators.

What would be displayed on the screen by the following code?

if (false)
{
    Console.WriteLine("Hello!");
}
Console.WriteLine("Hi!");

Is there a simpler way to write the expression over21 == true, assuming that over21 is a Boolean variable?
Assume that x and y are two int variables that have already been initialized (i.e., declared and assigned), write an if statement that assigns 10 to x if y is (strictly) greater than 5.
In C#, is there a difference between = and ==? Write a statement that uses =.
Assuming a name string was declared and initialized with a value given by the user, write an if statement that displays “I have the same name!” if name contains your first name.
Is the following statement correct, i.e., would it compile, assuming myFlag is a bool variable, and myAge is an initialized int variable?
```
if ( myAge > 20 )
{
    myFlag = true
};
```
If we write a statement that begins with if(false), then the IDE returns a warning, “Unreachable code detected”. What does it mean?
Write an if statement that prints “Bonjour !” if the value of the char variable lang is 'f'.
For each of the following boolean expressions, decide if it will evaluate to true or false when the boolean variables x, y and z are all set to true:
- x || y && z
- !x || y && z
- !(x || y) && (z && y)
- (!x && x) || (!x || x)
Do the same when they are all set to false.
Write a boolean expression that evaluates to true if a variable x is between 3 (excluded) and 5 (included).
Write an if-else statement that assigns 0.1 to z if y is greater or equal than 0, and that assigns −0.1 to z otherwise.
Write an if-else statement that assigns "Minor" to an already declared string variable legalStatus if age is strictly less than 18, and that assigns "Major" to legalStatus otherwise.
Write an if-else statement that displays “It’s free for you!” if an int variable age is between 0 and 18, and “It’s $5.00.” otherwise.
Assume we initialized an int variable called courseNumber and a string variable called courseCode. Write a series of statements that will display:
1. “I’m taking this class!” if courseNumber is 1301 and courseCode is CSCI;
2. “That’s my major!” if courseCode is CSCI;
3. “Is that an elective?” if courseNumber is greater than 3000; or
4. “Is it a good class?” otherwise.
Your program should display exactly one message.
Assume we previously initialized an int variable called graduationYear and a string variable called graduationSemester. Write a series of statements that will display:
1. “I will graduate at the same time!” if graduationYear is 2023 and graduationSemester is Fall;
2. “I love this season.” if graduationSemester is Spring;
3. “That is in a long time!” if graduationYear is greater than 2025; or
4. “I hope you’ll have an in-person ceremony!” otherwise.
Your program should display exactly one message.
Assume we previously initialized a char variable called myChar. Write a series of statements that will display if the character is…
1. Uppercase
2. Lowercase
3. A number
4. or none of those.
Your program should display exactly one message. Bonus: Make your message also display the ASCII value of the character.

What will be displayed on the screen by the following program?

int x = 3, y = 2, z = 4;
if (x > y) {z += y;}
if (x > z) {y -= 4;}
Console.WriteLine($"x is {x}, y is {y}, and z is {z}.");

What will be displayed on the screen by the following program?

int x = 3, y = 2, z = 4;
if (x >= z) {z += y;} else if (x != y) {z *= y;}
y -= 4;
Console.WriteLine($"x is {x}, y is {y}, and z is {z}.");

(We’ll use the 24-hour clock, sometimes called “military time”.) Assuming that an int variable hour has been initialized, write part of a program that would display on the screen “Good morning” if hours is less than or equal to 12, and “Hello” otherwise.
Assuming that myString is a string variable, write a statement that prints “Hello, Melody!” if the value of myString is equal to Melody, and nothing otherwise.

What will be displayed on the screen by the following program?

int x = 3, y = 2, z = 4;
if (y >= z) {z += y;}
else if (x != y) { if (false) {z -= 3;} else {z += x;}}
Console.WriteLine($"x is {x}, y is {y}, and z is {z}.");

Rewrite, if possible, the three following if-else-if statements as switch statements:

if (myLang == 'f')
{
    Console.WriteLine("Vous parlez Français ?");
}
else if (myLang == 'e')
{
    Console.WriteLine("Do you speak English?");
}
else if (myLang == 'd')
{
    Console.WriteLine("Sprechen Sie Deutsch?");
}
else
{
    Console.WriteLine("I do not know your language!");
}

if (myCity == "Augusta")
{
    Console.WriteLine("I also live here!");
}
else if (myCity == "Ithaca" || myCity == "Providence")
{
    Console.WriteLine("I used to live there!");
    }
else
{
    Console.WriteLine("I never lived there.");
}

if (temp == 100.0)
{
    Console.WriteLine("It's ready!");
}
else if (temp >= 90.0)
{
    Console.WriteLine("Almost ready!");
}
else
{
    Console.WriteLine("You have to wait.");
}

If you think it is not possible or not feasible, explain why.

Give an example of an if statement that could not be rewritten as a switch.

Part II – Problems

This time, the two exercises do not require a computer, and are here to craft on your problem-solving skills. Make sure you feel ready before starting them, try to do them with a limited amount of time and without notes, and check your answer using your IDE.

Write a program that asks the user to write a country name and stores the user’s input into a string variable. Then, compare that string with "france": if it is equal, then display at the screen "Bienvenue en France !". Then, compare that string with "usa": if it is equal, then display at the screen "Welcome to the US!". If the string is different from both "france" and "usa", then display at the screen "Welcome to" followed by the name of the country the user typed in. Can you think of two ways to implement this program, one using if-else-if statements, the other using switch?
You want to write a small program for an on-line printing company. Your program should ask the user to chose a format (10 × 15 centimeters, or 8 × 11 inches), ask if it is the first time the customer order through your company, and a number of copies. Then, calculate the total cost of printing those pictures, knowing that
- Printing a 10 × 15 centimeters picture costs $0.20, printing a 8 × 11 inches picture costs $0.25,
- A new customer gets a $3 coupon if the order is more than $5,
- A 10% discount is given if more than 50 copies were ordered,
- The two previous offers can be cumulated.
Display on the screen a message starting by “Welcome!”, then a new line, then “We cherish our new customers” if it is the first time the user uses your company, “, so we’re giving you a $3 discount!” if the user is allowed to get the coupon, then print the total and “You had a 10% discount!” if the user ordered more than 50 copies. See below for examples of execution, where the user input is underlined, and hitting carriage return is represented by ↵.
```
Enter 'c' for 10x15cm, anything else for 8x11in.
c͟ ↵
Is this your first time here? Type 'y' for 'yes'.
y͟ ↵
Enter a number of copies.
9͟0͟ ↵
Welcome!
We cherish our new customers, so we are giving you a $3 discount!
Your total is $13.50. You had a 10% discount!
```
```
Enter 'c' for 10x15cm, anything else for 8x11in.
p͟ ↵
Is this your first time here? Type 'y' for 'yes'.
N͟o͟t͟ ͟a͟t͟ ͟a͟l͟l͟↵
Enter a number of copies.
1͟2͟0͟ ↵
Your total is $27.00. You had a 10% discount!
```

Homework #5

Part I — Questions

Assume you are given an un-assigned string variable letterGrade, and an already assigned float variable numberGrade. Write a small program that assigns "A" to letterGrade if numberGrade is between 100 and 90 (both included), "B" to letterGrade if numberGrade is between 90 (excluded) and 80 (included), etc., and "Invalid data" if numberGrade is strictly lower than 0 or strictly greater than 100. Should you use a switch statement or a if …else if …else?
Given an int variable counter, write three statements to decrement its value by 1.

What will be displayed on the screen?

int x = 3, y = 7;
Console.WriteLine (x++ +" and "+ --y);

What will be displayed on the screen by the following program?

int counter = 2;
while (counter != 5)
{
    Console.Write(counter + "\n");
    counter++;
}

What will be displayed on the screen by the following program? Write the spaces and new line explicitly.

int counter = 10;
while (counter > 5)
{
    counter--;
    Console.Write(counter + "\n");
    if (counter == 7) {
        Console.WriteLine("Bingo");
    }
}

What will be displayed on the screen by the following program?

int counter = 10;
while (counter != 5) ;
Console.Write(counter + "\n");
counter--;

What will be displayed on the screen by the following program?

int counter = 7;
while (counter != 2)
    Console.Write(counter + "\n");
counter--;

What is input validation? Name a control structure that can be used to perform it. Why is it important?
What do we name a variable that is increased by some value at every iteration of a loop, i.e., that keeps the running total?
What is a sentinel value?
Write a program that asks the user to enter a value between 0 and 10, and asks again as long as the user enters integers outside that range.
Write a small program that asks the user for an integer, and displays “It is positive” if the number entered is positive, “It is negative” if the number entered is negative, and “Not a number” if the user entered a string that is not an integer.
Write a program containing a while loop that would display the numbers between -100 and 100 (both included) with a space between them when executed.
Assume you are given an initialized string variable name, and a string variable field. Write a small program that assigns to field
- “CS” if name is “Turing” or “Liskov”,
- “Math.” if name is “Aryabhata” or “Noether”,
- “Unknown” otherwise.
Write a program that asks the user to enter a value between 1900 and 1999 (both included), and asks again as long as the user enters integers outside that range.

Part II – Problems

Write a switch statement that calculates the number of days in a particular month. You should assume that you are given already assigned month and year int variables, and that your program should set an already declared int numberOfDays variable to 28, 29, 30 or 31 depending on the month / year combination. Your program should start with a switch matching month against certain values, and, if month is 2, uses an if statement to decide whenever the number of days is 28 or 29. You can use something like
```
switch (month) {
    …
    case (2):
        if …
        …
        break;
    …
}
```

Homework #6

Part I — Questions

Write a statement that creates a 10-element int array named numbers.
In the following, what is the value of the size declarator? What is the value of the index?
```
int[] numbers;
numbers = new int[8];
numbers[4] = 9;
```
What is wrong with the following array declaration?
```
int[] books = new int[-1];
```
Draw the content of the scores array once those statements have been executed.
```
int[] scores = new int[3];
scores[0] = 13;
scores[2] = 25;
```

What will be displayed on the screen by the following program?

for (int num = 3 ; num <= 5 ; num++)
    Console.Write(num + " ");

Write a ‘for’ loop that displays on the screen the sequence “1, 2, 3, 4, 5, 6, 7, 8, 9, 10, ”.
Write a ‘for’ loop that displays on the screen the sequence “1, 2, 3, 4, 5, 6, 7, 8, 9, 10”, (note that there is no comma after 10).
Write a ‘for’ loop that displays on the screen the sequence “1 3 5 7 9 ”.
Given an int variable myVar initialized with a positive value, write a loop that sums the integers between 0 and myVar (i.e., 0 + 1 + ⋯ + (myVar − 1) + myVar).
Consider the following code:
```
for (int y = 1; y <= 3; y++)
{
    for (int z = 1; z < 5; z++)
        Console.Write("Scene " + y + ", take " + z + ". " );
    Console.WriteLine();
}
```
How many times does the outer loop iterate (i.e., how many scenes are shot)? How many times does the inner loop iterate (i.e., how many takes for each scene)? Finally, what is the total number of iterations of the nested loops (i.e., how many takes are made, total)?
Which of the following are pre-test loops? do while, switch, while, for and if-else-if.

What will be displayed on the screen by the following code?

int[] values = new int[6];
for (int i = 0 ; i < 6 ; i++)
    values[i] = (i*2);
foreach (int j in values)
    Console.WriteLine(j);

Suppose we are given an int array dailyPushUp with 7 elements. Write a piece of code that display the value of the elements stored in the array dailyPushUp.
What is “array bounds checking”? When does it happen?
What would be the size of the test array after the following statement has been executed?
```
int[] test = {3, 5, 7, 0, 9};
```
What is the difference, if any, between the following two statements?
```
int[] num, scores;
int num[], scores;
```
Write a statement that creates and initializes a double array with the values 12.5, 89.0 and 3.24.
What is the value of count and the content of number once the following has been executed?
```
int count=2;
int[] number={3, 5, 7};
number[count--] = 8;
number[count]--;
```
Suppose we have an array named temp that has been declared and initialized. How can we get the number of elements in this array?

Describe what the following code would do.

int[] record = { 3, 8, 11 };
int accumulator = 0;
foreach (int i in record)
    accumulator += i;

Assuming we have two int arrays of the same size, firstA and secondA, write a program that copies the content of firstA into secondA.
Assuming we are given an int array named arrayF, write a program that adds one to each of its elements. That is, if arrayF contains 3, 5, 7 and -2 before your program is executed, it should then contain 4, 6, 8 and -1 after your program was executed.
Assuming we are given an int array named arrayF, write a program that displays the product of its elements. That is, if arrayF contains 2, 3 and -1, then your program should display -6.
Write a static method (header included) that takes as argument an int array, and display on the screen the value of each element of that array.
Write a static method (header included) that takes as argument an int array, and stores the value 10 in each element of that array.

Quizzes

Those quizzes are given as examples, to help you practise. They were given at week 4 and 7.

Quiz 1

(3 pts) List three keywords.
(4pts) Circle the correct identifiers:
- %Rate
- static
- my-variable
- User.Input
- YoUrNaMe21
- test_train
- _myIdentifier

(4 pts) For each of the following, indicate if they are a “rule” of C# or a “convention” between programers by ticking the appropriate column. The first answer is given as an example.

Statement	Rule	Convention
Code should be commented.		✓
Case matters.
Variable names should be descriptive.
Keywords cannot be used as identifiers.
Each “.cs” file should contain exactly one class.

(4 pts) Write a statement that would display, “Hi Mom!” (with the quotes) followed by a new line on the screen.
(5 pts) Write a series of statements that would
1. declare an int variable called “myAge”,
2. assign your age to that variable,
3. display “My age is”, the value of the “myAge” variable, a period, and finally a new line.
(Bonus) Give examples of situations where the adage “Spaces and new lines do not matter in programs” is actually erroneous.

Quiz 2

(2 pts) What is the relational operator used to determine whenever two values are equal?
(2 pts) Write a boolean expression that evaluates to true if a variable yourName is different from "Marc" and "Mark".
(5pts) Write a boolean expression that evaluates to true if a variable x is between -10 (excluded) and 10 (included).

(3 pts) What will be displayed on the screen by the following program?

int x = 5, y = 1, z = 2;
if (x != z || y < z ) {x += y;}
if (z > y) {if (z % 2 == 0) {z -= 3;} else {z += x;}} else {x = y + z;}
Console.WriteLine($"x is {x}, y is {y}, and z is {z}.");

(8 pts) Assume we initialized a string variable named month and a double variable named temperature. Write a series of statements that will display exactly one of the following messages: “What a nice summer day!” if month is “July” and temperature is less than 90 (included); “Better wear a jacket” if temperature is between 45 and 60 (both included); “Happy holidays!” if month is “December”; or “Have a nice day” otherwise.
(Bonus) Give a program that displays “Leap year” if a year variable is
1. divisible by 4; and
2. not divisible by 100, unless it is also divisible by 400.
Your program should correctly identify 2000 and 2400 as leap years, and 1800, 1900, 2100, 2200, 2300, or 2500 as not leap years.

Quiz 3

(7 pts) Write a switch statement that sets a decimal price variable to 1.50 if a string variable iceCreamFlavor contains "vanilla", 1.75 if it contains "chocolate" or "mint", and -1 otherwise.
(2 pts) Write a statement that applies the increment operator in prefix position to a variable test.
(3 pts) What will be displayed on the screen by the following program?
```
int x = 10;
x--;
while(x > 0){
    Console.Write(x);
}
```
(8 pts) Write a while loop that displays “1 2 3 4 5 6 7 8 9 10 11 12 13” (spaces included!) at the screen.
(+3+2 pt, bonus) Give a program that displays every multiple of 3 between 0 and 10,000 (that is, “0 3 6 9 12 … 9999”). Bonus (again!): display how many such numbers there are in total.