Runtime cost of dynamic type resolution in C Sharp (C#) - Interactive Code Practice

Practice - 5 Tasks

1fill in blank

easy

Complete the code to declare a dynamic variable.

C Sharp (C#)

dynamic value = [1];

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

Anull

B"text"

Ctrue

D10

Attempts:

3 left

💡 Hint

Common Mistakes

Using quotes around 10 makes it a string, not an integer.

The dynamic keyword allows the variable to hold any type. Here, assigning the integer 10 is valid.

2fill in blank

medium

Complete the code to access the length property on a dynamic variable.

C Sharp (C#)

dynamic obj = "hello";
int length = obj.[1];

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

ALength

Blength

CCount

DGetLength

Attempts:

3 left

💡 Hint

Common Mistakes

Using Count is for collections, not strings.

The Length property returns the number of characters in a string. When using dynamic, this is resolved at runtime.

3fill in blank

hard

Fix the error in the dynamic method call.

C Sharp (C#)

dynamic obj = 123;
string text = obj.[1]();

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AtoString

BToString

CConvert

DParse

Attempts:

3 left

💡 Hint

Common Mistakes

Using lowercase 'toString' causes a runtime error.

The method ToString() converts the integer to its string representation. It is case-sensitive and must be capitalized.

4fill in blank

hard

Fill both blanks to create a dictionary with dynamic keys and values.

C Sharp (C#)

var dict = new Dictionary<[1], [2]>();

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Adynamic

Bstring

Cint

Dobject

Attempts:

3 left

💡 Hint

Common Mistakes

Mixing static types like string or int causes type errors.

Using dynamic for both key and value types allows runtime type resolution for dictionary entries.

5fill in blank

hard

Fill all three blanks to create a dynamic method call with runtime type resolution.

C Sharp (C#)

dynamic obj = GetDynamicObject();
var result = obj.[1]([2]: [3]);

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

ACalculate

Bvalue

C42

DExecute

Attempts:

3 left

💡 Hint

Common Mistakes

Using wrong method names or parameter names causes runtime errors.

The method Calculate is called with a named parameter value set to 42. This call is resolved at runtime due to dynamic.

Practice

1. What does dynamic keyword in C# do at runtime?

easy

A. It performs type checking at compile time

B. It prevents any type errors completely

C. It delays type checking until the program runs

D. It converts all types to strings automatically

Solution

1. Step 1: Understand the role of dynamic

   The dynamic keyword tells C# to skip compile-time type checking for that variable.

2. Step 2: Identify when type checking happens

   Type checking for dynamic variables happens only when the program runs, not before.

3. Final Answer:

   It delays type checking until the program runs -> Option C

4. Quick Check:

   Dynamic = runtime type check [OK]

Hint: Dynamic means check types only when running [OK]

Common Mistakes:

• Thinking dynamic checks types at compile time
• Believing dynamic prevents all errors
• Assuming dynamic converts types automatically

2. Which of the following is the correct syntax to declare a dynamic variable in C#?

easy

A. dynamic = 5 x;

B. var x = dynamic 5;

C. int dynamic x = 5;

D. dynamic x = 5;

Solution

1. Step 1: Recall dynamic variable declaration syntax

   In C#, you declare a dynamic variable by writing dynamic followed by the variable name and value.

2. Step 2: Check each option's syntax

   dynamic x = 5; matches the correct syntax: dynamic x = 5;. Others have incorrect order or keywords.

3. Final Answer:

   dynamic x = 5; -> Option D

4. Quick Check:

   Correct syntax = dynamic x = value [OK]

Hint: Use 'dynamic' before variable name [OK]

Common Mistakes:

• Putting 'dynamic' after 'var'
• Mixing 'int' and 'dynamic' keywords
• Incorrect order of assignment

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

dynamic x = 10;
dynamic y = "20";
Console.WriteLine(x + y);

medium

A. 1020

B. Runtime exception

C. 30

D. Compile-time error

Solution

1. Step 1: Analyze the types of variables

   Variable x is an integer 10, and y is a string "20".

2. Step 2: Understand dynamic addition behavior

   With dynamic types, the + operator at runtime performs string concatenation when one operand is a string, resulting in "1020".

3. Final Answer:

   1020 -> Option A

4. Quick Check:

   dynamic int + string = concatenation "1020" [OK]

Hint: Dynamic number + string = string concatenation [OK]

Common Mistakes:

• Expecting a runtime exception
• Thinking it adds numerically to 30
• Assuming compile-time error

4. Identify the error in this code snippet using dynamic types:

dynamic a = 5;
dynamic b = "hello";
var result = a - b;
Console.WriteLine(result);

medium

A. Runtime exception due to invalid operation

B. No error, outputs 0

C. Compile-time type mismatch error

D. Syntax error in variable declaration

Solution

1. Step 1: Check operation between dynamic variables

   Subtracting an integer and a string is invalid at runtime.

2. Step 2: Determine error type

   Since types are dynamic, error appears only when running, causing a runtime exception.

3. Final Answer:

   Runtime exception due to invalid operation -> Option A

4. Quick Check:

   Invalid dynamic operation = runtime exception [OK]

Hint: Invalid dynamic operations fail at runtime, not compile time [OK]

Common Mistakes:

• Expecting compile-time error
• Assuming subtraction works with string
• Ignoring runtime exceptions

5. You want to improve performance in a C# program that uses many dynamic variables. Which approach reduces runtime cost of dynamic type resolution?

hard

A. Avoid testing dynamic code to save time

B. Replace dynamic variables with explicit static types where possible

C. Add more dynamic variables to delay errors

D. Use dynamic variables everywhere for flexibility

Solution

1. Step 1: Understand runtime cost of dynamic

   Dynamic variables cause extra work at runtime to check types, slowing performance.

2. Step 2: Choose optimization strategy

   Replacing dynamic with static types lets compiler check types early, improving speed.

3. Final Answer:

   Replace dynamic variables with explicit static types where possible -> Option B

4. Quick Check:

   Static types reduce dynamic runtime cost [OK]

Hint: Use static types to speed up dynamic-heavy code [OK]

Common Mistakes:

• Thinking more dynamic variables improve speed
• Ignoring testing importance
• Believing dynamic has no runtime cost