Default values for types in C Sharp (C#) - Mini Project: Build & Apply

Default values for types

📖 Scenario: Imagine you are creating a simple program to understand what default values different types have in C#. This helps when you declare variables but don't assign values yet.

🎯 Goal: You will create variables of different types and print their default values to see what C# assigns automatically.

📋 What You'll Learn

Create variables of type int, bool, and string without assigning values.

Create a variable called defaultInt and set it to the default value of int using default keyword.

Create a variable called defaultBool and set it to the default value of bool using default keyword.

Create a variable called defaultString and set it to the default value of string using default keyword.

Print the values of defaultInt, defaultBool, and defaultString.

💡 Why This Matters

🌍 Real World

Knowing default values helps when you declare variables and want to understand what initial values they hold before assignment.

💼 Career

Understanding default values is important for debugging and writing safe code that avoids unexpected behaviors.

1

Create variables without assigning values

Create variables called number of type int, flag of type bool, and text of type string without assigning any values.

C Sharp (C#)

// Declare variables without assigning values
int number;
bool flag;
string text;
// Your code here

Hint

Just declare the variables with their types and names, but do not assign any values.

2

Assign default values using default keyword

Create variables called defaultInt, defaultBool, and defaultString. Assign them the default values of int, bool, and string respectively using the default keyword.

C Sharp (C#)

int number;
bool flag;
string text;
// Assign default values
int defaultInt = default(int);
bool defaultBool = default(bool);
string defaultString = default(string);
// Your code here

Hint

Use the syntax type variable = default(type); to get the default value for each type.

3

Print the default values

Use Console.WriteLine to print the values of defaultInt, defaultBool, and defaultString each on its own line.

C Sharp (C#)

int number;
bool flag;
string text;
int defaultInt = default(int);
bool defaultBool = default(bool);
string defaultString = default(string);
// Print the default values
Console.WriteLine(defaultInt);
Console.WriteLine(defaultBool);
Console.WriteLine(defaultString);
// Your code here

Hint

Use Console.WriteLine(variable); to print each variable's value.

4

Run the program to see the output

Run the program and observe the output. It should print the default values of int, bool, and string types in order.

C Sharp (C#)

int number;
bool flag;
string text;
int defaultInt = default(int);
bool defaultBool = default(bool);
string defaultString = default(string);
Console.WriteLine(defaultInt);
Console.WriteLine(defaultBool);
Console.WriteLine(defaultString);
// Run the program to see output

Hint

The output shows 0 for int, False for bool, and an empty line for string because its default is null.

Practice

1. What is the default value of an int type variable in C#?

easy

A. 0

B. null

C. 1

D. "" (empty string)

Solution

1. Step 1: Understand default values for value types

   In C#, value types like int have a default value of zero when not initialized.

2. Step 2: Recall default for int

   The default for int is 0, not null or any other value.

3. Final Answer:

   0 -> Option A

4. Quick Check:

   Default int = 0 [OK]

Hint: Remember: numbers default to zero in C# [OK]

Common Mistakes:

• Thinking default int is null
• Confusing default int with 1
• Assuming default is empty string

2. Which of the following is the correct syntax to get the default value of a type T in C#?

easy

A. T.default()

B. default = T

C. default(T)

D. T.default

Solution

1. Step 1: Recall C# syntax for default values

   The correct syntax to get the default value of a type T is default(T).

2. Step 2: Check other options

   Options like T.default(), default = T, and T.default are invalid syntax in C#.

3. Final Answer:

   default(T) -> Option C

4. Quick Check:

   Use default(T) to get default value [OK]

Hint: Use default(Type) syntax to get default value [OK]

Common Mistakes:

• Using invalid syntax like T.default()
• Confusing assignment with default keyword
• Trying to access default as a property

3. What will be the output of this C# code?

bool flag = default;
Console.WriteLine(flag);

medium

A. False

B. null

C. True

D. Compilation error

Solution

1. Step 1: Understand default value of bool

   The default value of bool in C# is false.

2. Step 2: Analyze the code output

   The variable flag is assigned default, so it holds false. Printing it outputs "False".

3. Final Answer:

   False -> Option A

4. Quick Check:

   Default bool = false [OK]

Hint: Default bool is always false, not true [OK]

Common Mistakes:

• Assuming default bool is true
• Expecting null for bool
• Thinking code causes error

4. Identify the error in this C# code snippet:

string text = default;
int number = default;
Console.WriteLine(text.Length);

medium

A. Compile-time error on text.Length

B. No error, code runs fine

C. Syntax error on default keyword

D. NullReferenceException at runtime

Solution

1. Step 1: Understand default for reference types

   For reference types like string, default is null.

2. Step 2: Analyze accessing property on null

   Accessing text.Length when text is null causes a NullReferenceException at runtime.

3. Final Answer:

   NullReferenceException at runtime -> Option D

4. Quick Check:

   Default string = null; accessing Length causes error [OK]

Hint: Default reference types are null; accessing members causes errors [OK]

Common Mistakes:

• Thinking default string is empty string
• Expecting compile-time error instead of runtime
• Ignoring null checks before member access

5. Given this struct and code:

struct Point { public int X; public int Y; }
Point p = default;
Console.WriteLine(p.X + "," + p.Y);

What is the output and why?

hard

A. Random values because struct fields are not set

B. 0,0 because struct fields default to zero

C. Compilation error because fields are uninitialized

D. null,null because struct is a reference type

Solution

1. Step 1: Understand default for structs

   Structs are value types; their fields get default values when using default.

2. Step 2: Default values of int fields in struct

   Both X and Y are int, so default is 0 for each.

3. Step 3: Output concatenation

   Printing p.X + "," + p.Y outputs "0,0".

4. Final Answer:

   0,0 because struct fields default to zero -> Option B

5. Quick Check:

   Struct fields default to zero [OK]

Hint: Struct fields default to zero, not null [OK]

Common Mistakes:

• Thinking structs are reference types
• Expecting null values for struct fields
• Assuming uninitialized fields cause errors