Type conversion and casting in C Sharp (C#) - Mini Project: Build & Apply

Type conversion and casting

📖 Scenario: You are working on a simple program that handles different types of numbers. Sometimes you need to convert numbers from one type to another to make calculations or display results correctly.

🎯 Goal: Build a program that converts and casts numbers between int, double, and string types, demonstrating how to change data types safely and correctly.

📋 What You'll Learn

Create an integer variable with a specific value

Create a double variable with a specific value

Convert the integer to a double using casting

Convert the double to an integer using casting

Convert the integer to a string using type conversion

Print all converted values to show the results

💡 Why This Matters

🌍 Real World

Type conversion and casting are common when working with user input, calculations, and displaying data in different formats.

💼 Career

Understanding how to convert and cast types is essential for software developers to avoid errors and write clear, correct code.

1

Create initial number variables

Create an int variable called myInt and set it to 42. Create a double variable called myDouble and set it to 3.14.

C Sharp (C#)

// Create an int variable called myInt and set it to 42
// Create a double variable called myDouble and set it to 3.14
// Your code here

Hint

Use int myInt = 42; and double myDouble = 3.14; to create the variables.

2

Add variables for casting and conversion

Create a double variable called castedDouble and set it by casting myInt to double. Create an int variable called castedInt and set it by casting myDouble to int.

C Sharp (C#)

int myInt = 42;
double myDouble = 3.14;
// Create a double variable castedDouble by casting myInt to double
// Create an int variable castedInt by casting myDouble to int
// Your code here

Hint

Use (double)myInt to cast int to double and (int)myDouble to cast double to int.

3

Convert integer to string

Create a string variable called intAsString and set it by converting myInt to a string using the ToString() method.

C Sharp (C#)

int myInt = 42;
double myDouble = 3.14;
double castedDouble = (double)myInt;
int castedInt = (int)myDouble;
// Convert myInt to string and store in intAsString
// Your code here

Hint

Use myInt.ToString() to convert the integer to a string.

4

Print all converted values

Print the values of castedDouble, castedInt, and intAsString each on a new line using Console.WriteLine().

C Sharp (C#)

int myInt = 42;
double myDouble = 3.14;
double castedDouble = (double)myInt;
int castedInt = (int)myDouble;
string intAsString = myInt.ToString();
// Print castedDouble
// Print castedInt
// Print intAsString
// Your code here

Hint

Use Console.WriteLine() to print each variable on its own line.

Practice

1. What is the main difference between type conversion and casting in C#?

easy

A. Casting changes data to string only, conversion changes data to numbers only.

B. Casting is automatic, conversion always requires manual code.

C. Casting requires compatible types and uses parentheses, conversion can be safer and more flexible.

D. Casting works only with classes, conversion works only with structs.

Solution

1. Step 1: Understand casting in C#

   Casting uses parentheses and works only when types are compatible, like int to double or object to string.

2. Step 2: Understand conversion methods

   Conversion methods like Convert.ToInt32 or int.Parse are safer and can handle strings and other types more flexibly.

3. Final Answer:

   Casting requires compatible types and uses parentheses, conversion can be safer and more flexible. -> Option C

4. Quick Check:

   Casting vs Conversion = Casting requires compatible types and uses parentheses, conversion can be safer and more flexible. [OK]

Hint: Casting uses parentheses; conversion uses methods like Convert.ToInt32 [OK]

Common Mistakes:

• Thinking casting works with all types automatically
• Confusing conversion methods with casting syntax
• Assuming casting changes data format like conversion

2. Which of the following is the correct syntax to cast a double variable d to an int in C#?

easy

A. int i = (int)d;

B. int i = int(d);

C. int i = Convert.ToInt(d);

D. int i = d as int;

Solution

1. Step 1: Recall casting syntax in C#

   Casting uses parentheses with the target type before the variable, like (int)d.

2. Step 2: Check each option

   int i = (int)d; uses correct casting syntax. int i = int(d); is invalid syntax. int i = Convert.ToInt(d); uses wrong method name (should be Convert.ToInt32). int i = d as int; uses 'as' which works only with reference types.

3. Final Answer:

   int i = (int)d; -> Option A

4. Quick Check:

   Correct cast syntax = int i = (int)d; [OK]

Hint: Casting uses (type)variable syntax, not functions or 'as' keyword [OK]

Common Mistakes:

• Using 'as' keyword for value types
• Calling non-existent Convert.ToInt method
• Using function-like syntax for casting

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

double d = 9.7;
int i = (int)d;
Console.WriteLine(i);

medium

A. Compilation error

B. 10

C. 9.7

D. 9

Solution

1. Step 1: Understand casting from double to int

   Casting double to int truncates the decimal part, it does not round.

2. Step 2: Apply casting to value 9.7

   Truncating 9.7 results in 9, so i = 9.

3. Final Answer:

   9 -> Option D

4. Quick Check:

   Double to int cast truncates decimals = 9 [OK]

Hint: Casting double to int drops decimals, no rounding [OK]

Common Mistakes:

• Assuming casting rounds the number
• Expecting a compilation error
• Confusing output with original double value

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

string s = "123abc";
int num = Convert.ToInt32(s);
Console.WriteLine(num);

medium

A. FormatException at runtime due to invalid string format

B. num will be 0 because of invalid characters

C. Compilation error because Convert.ToInt32 does not exist

D. No error, code runs and prints 123

Solution

1. Step 1: Understand Convert.ToInt32 behavior

   Convert.ToInt32 tries to convert the whole string to an integer and throws an exception if format is invalid.

2. Step 2: Analyze string "123abc"

   String contains non-digit characters, so conversion fails and throws FormatException at runtime.

3. Final Answer:

   FormatException at runtime due to invalid string format -> Option A

4. Quick Check:

   Invalid string format causes FormatException [OK]

Hint: Convert.ToInt32 throws error if string has non-digit chars [OK]

Common Mistakes:

• Assuming partial conversion succeeds
• Expecting zero instead of exception
• Thinking Convert.ToInt32 is compile-time error

5. You have an object obj that holds an integer value. Which code safely converts obj to an int without risking an exception if obj is not an int?

hard

A. int i = Convert.ToInt32(obj);

B. int i = obj is int val ? val : 0;

C. int i = obj as int;

D. int i = (int)obj;

Solution

1. Step 1: Understand casting and conversion risks

   Direct cast (int)obj throws exception if obj is not int. Convert.ToInt32 may throw exceptions too. 'as' cannot be used with value types like int.

2. Step 2: Analyze safe pattern

   Using pattern matching with 'is' checks type safely and assigns value or default 0 if not int, avoiding exceptions.

3. Final Answer:

   int i = obj is int val ? val : 0; -> Option B

4. Quick Check:

   Pattern matching safely converts or defaults = int i = obj is int val ? val : 0; [OK]

Hint: Use 'is' pattern matching to safely cast without exceptions [OK]

Common Mistakes:

• Using 'as' with value types causing compile errors
• Casting without checking type causing exceptions
• Assuming Convert.ToInt32 always safe