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+---
+title: "C#: Basics - Answer Key"
+date: 2026-04-27T00:00:00-07:00
+draft: false
+weight: 15
+hidden: true
+---
+
+{{% notice note %}}
+These are sample solutions. Many challenges have multiple valid answers, especially those that ask you to create your own examples. Your solution is correct if it produces the expected output!
+{{% /notice %}}
+
+## Variables and Data Types
+
+### Help Patrick Fix His Variables
+
+Patrick's code has the wrong data types assigned to each variable. Here are the corrected declarations:
+
+```csharp
+string bestFriend = "Minerva";
+int numOfFriends = 4;
+double GPA = 3.6;
+char meaningOfLife = '$';
+bool loveMusic = true;
+```
+
+**Explanation:** Each variable needs a data type that matches the value being stored:
+
+| Variable | Wrong Type | Correct Type | Why |
+|----------|-----------|-------------|-----|
+| `bestFriend` | `int` | `string` | `"Minerva"` is text, not a number |
+| `numOfFriends` | `bool` | `int` | `4` is a whole number, not true/false |
+| `GPA` | `string` | `double` | `3.6` is a decimal number, not text |
+| `meaningOfLife` | `double` | `char` | `'$'` is a single character, not a decimal |
+| `loveMusic` | `char` | `bool` | `true` is a boolean value, not a character |
+
+Output:
+```
+You fixed it!
+```
+
+## Operators
+
+### Exam Statistics
+
+Given the grades: Patrick (88), Tom (89), Mary (95), Chris (84), Jen (92):
+
+```csharp
+// 1. Declare student grade variables
+int patrickGrade = 88;
+int tomGrade = 89;
+int maryGrade = 95;
+int chrisGrade = 84;
+int jenGrade = 92;
+
+// 2. Calculate the class average
+average = (patrickGrade + tomGrade + maryGrade + chrisGrade + jenGrade) / 5.0;
+
+// 3. Use relational operators for the comparisons
+bool over60 = average > 60;
+bool over70 = average > 70;
+bool over80 = average > 80;
+bool over90 = average > 90;
+```
+
+{{% notice tip %}}
+We divide by `5.0` instead of `5` to get a decimal result. In C#, dividing two integers gives an integer (the remainder is thrown away). Using `5.0` ensures we get the exact average.
+{{% /notice %}}
+
+Output:
+```
+---------------------------
+     Music Grade Report    
+---------------------------
+
+Student Grades:          
+- Patrick: 88
+- Tom: 89
+- Mary: 95
+- Chris: 84
+- Jen: 92
+
+Class Average: 89.6
+- Average Over 60: True
+- Average Over 70: True
+- Average Over 80: True
+- Average Over 90: False
+```
+
+## Control Structures
+
+### If-Statement: Patrick's Greeting
+
+Fill in the boolean expressions so Patrick says the right greeting based on the hour:
+
+```csharp
+int currentHour = 10; // change this to test different hours (0-23)
+
+if (currentHour < 12)
+{
+    Console.WriteLine("Good Morning");
+}
+else if (currentHour < 20)
+{
+    Console.WriteLine("Good Afternoon");
+}
+else
+{
+    Console.WriteLine("Good Night");
+}
+```
+
+**How it works:**
+- Hours 0-11: `currentHour < 12` is `true` → prints "Good Morning"
+- Hours 12-19: `currentHour < 12` is `false`, but `currentHour < 20` is `true` → prints "Good Afternoon"
+- Hours 20-23: both conditions are `false` → falls into `else` → prints "Good Night"
+
+### For-Loop: Sum of 1 to 100
+
+Convert the while loop to a for loop that calculates 1 + 2 + 3 + ... + 100:
+
+```csharp
+int total = 0;
+for (int num = 1; num <= 100; num = num + 1)
+{
+    total = total + num;
+}
+Console.WriteLine("Answer calculated in a for loop: " + total);
+```
+
+Output:
+```
+Answer calculated in a for loop: 5050
+```
+
+{{% notice tip %}}
+The answer is 5050. A famous story says the mathematician Carl Friedrich Gauss figured this out as a child by noticing that 1 + 100 = 101, 2 + 99 = 101, and so on — giving 50 pairs of 101, which equals 5050!
+{{% /notice %}}
+
+## Methods
+
+### Count the Pyramid
+
+Write a method that calculates the total number of beads in a square-number pyramid with `n` levels. Level 1 has 1×1 = 1 bead, level 2 has 2×2 = 4 beads, level 3 has 3×3 = 9 beads, and so on.
+
+```csharp
+public static int pyramidCount(int levels)
+{
+    int total = 0;
+    for (int i = 1; i <= levels; i++)
+    {
+        total = total + (i * i);
+    }
+    return total;
+}
+```
+
+**How it works:** The method loops through each level from 1 to `levels`, adding the square of the level number (`i * i`) to the running total.
+
+Example values:
+
+| Levels | Calculation | Total |
+|--------|------------|-------|
+| 1 | 1×1 | 1 |
+| 2 | 1 + 4 | 5 |
+| 3 | 1 + 4 + 9 | 14 |
+| 4 | 1 + 4 + 9 + 16 | 30 |
+
+Output:
+```
+Congratulations! Challenge Solved!
+```
+
+## Classes and Objects
+
+### Build the Bird Class
+
+Here is the complete `Bird` class with all fields, the constructor, and all methods:
+
+```csharp
+public class Bird
+{
+    // Step 1: Declare private fields
+    private string species;
+    private string name;
+    private string hobby;
+    private int age;
+    private bool loveMusic;
+
+    // Step 2: Constructor
+    public Bird(string speciesInput, string nameInput, string hobbyInput, int ageInput, bool loveMusicInput)
+    {
+        species = speciesInput;
+        name = nameInput;
+        hobby = hobbyInput;
+        age = ageInput;
+        loveMusic = loveMusicInput;
+    }
+
+    // Step 3: Getter methods
+    public string getSpecies()
+    {
+        return species;
+    }
+
+    public string getName()
+    {
+        return name;
+    }
+
+    public string getHobby()
+    {
+        return hobby;
+    }
+
+    public int getAge()
+    {
+        return age;
+    }
+
+    public bool getLoveMusic()
+    {
+        return loveMusic;
+    }
+
+    // Step 4: ToString method
+    public string ToString()
+    {
+        string info = "";
+        info = info + "Hi, my name is " + getName() +
+               ". I am a " + getAge() + " year old " + getSpecies() +
+               " who likes to " + getHobby() + ". ";
+
+        if (getLoveMusic())
+        {
+            info = info + "I also like music very much!";
+        }
+        else
+        {
+            info = info + "However, I do not like music!";
+        }
+
+        return info;
+    }
+}
+```
+
+Output:
+```
+Congratulations! You correctly implemented the Bird Class :)
+```
+
+### Creating Bird Objects
+
+Once you have the `Bird` class, you can create Bird objects and print their information:
+
+```csharp
+Bird patrick = new Bird("duck", "Patrick", "swimming", 15, true);
+Bird sally = new Bird("swan", "Sally", "reading", 10, false);
+Bird oscar = new Bird("owl", "Oscar", "stargazing", 20, true);
+
+Console.WriteLine(patrick.ToString());
+Console.WriteLine(sally.ToString());
+Console.WriteLine(oscar.ToString());
+```
+
+Example output:
+```
+Hi, my name is Patrick. I am a 15 year old duck who likes to swimming. I also like music very much!
+Hi, my name is Sally. I am a 10 year old swan who likes to reading. However, I do not like music!
+Hi, my name is Oscar. I am a 20 year old owl who likes to stargazing. I also like music very much!
+```
+
+{{% notice note %}}
+You can create birds with any species, name, hobby, age, and music preference you like! The examples above are just one possibility.
+{{% /notice %}}