Type conversion and casting in C Sharp (C#) - Interactive Code Practice

Practice - 5 Tasks

1fill in blank

easy

Complete the code to convert an integer to a double.

C Sharp (C#)

int number = 10;
double result = (double)[1];
Console.WriteLine(result);

Drag options to blanks, or click blank then click option'

AConvert

Bresult

C10

Dnumber

Attempts:

3 left

💡 Hint

Common Mistakes

Using the target variable name instead of the source variable.

Trying to cast a method or keyword instead of the variable.

We cast the integer variable number to a double using (double)number.

2fill in blank

medium

Complete the code to convert a string to an integer using a built-in method.

C Sharp (C#)

string text = "123";
int number = [1](text);
Console.WriteLine(number);

Drag options to blanks, or click blank then click option'

AParse

BToString

CConvert.ToDouble

DToInt32

Attempts:

3 left

💡 Hint

Common Mistakes

Using ToString which converts to string, not integer.

Using Convert.ToDouble which converts to double, not int.

The int.Parse() method converts a string to an integer.

3fill in blank

hard

Fix the error in the code to safely convert a string to an integer using TryParse.

C Sharp (C#)

string input = "456";
if (int.[1](input, out int result))
{
    Console.WriteLine(result);
}
else
{
    Console.WriteLine("Conversion failed");
}

Drag options to blanks, or click blank then click option'

ATryParse

BToInt32

CConvert

DParse

Attempts:

3 left

💡 Hint

Common Mistakes

Using Parse which throws exceptions on failure.

Using Convert which does not have TryParse.

int.TryParse() attempts to convert a string to int safely without throwing exceptions.

4fill in blank

hard

Fill both blanks to convert a double to an integer using casting and print the result.

C Sharp (C#)

double value = 9.78;
int intValue = ([1]) value;
Console.WriteLine([2]);

Drag options to blanks, or click blank then click option'

Aint

Bvalue

CintValue

Ddouble

Attempts:

3 left

💡 Hint

Common Mistakes

Casting to double instead of int.

Printing the original double variable instead of the casted int.

We cast the double value to int and print the integer variable intValue.

5fill in blank

hard

Fill all three blanks to create a dictionary with string keys and integer values, filtering only values greater than 10.

C Sharp (C#)

var data = new Dictionary<string, int> { {"a", 5}, {"b", 15}, {"c", 25} };
var filtered = data.Where(kv => kv.Value [1] 10)
               .ToDictionary(kv => kv.[2], kv => kv.[3]);
foreach (var item in filtered)
{
    Console.WriteLine($"{item.Key}: {item.Value}");
}

Drag options to blanks, or click blank then click option'

A>

BKey

CValue

D<

Attempts:

3 left

💡 Hint

Common Mistakes

Using less than operator which filters wrong entries.

Mixing up Key and Value in the dictionary creation.

The code filters dictionary entries where the value is greater than 10, then creates a new dictionary using the original keys and values.

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