How Strings Work Differently Across Languages in DSA C# - Code Step by Step

Practice - 5 Tasks

1fill in blank

easy

Complete the code to create a string variable named greeting with the value "Hello".

DSA C#

string greeting = [1];

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

A'Hello'

Bnew String("Hello")

CHello

D"Hello"

Attempts:

3 left

💡 Hint

Common Mistakes

Using single quotes instead of double quotes for strings.

Trying to create a string without quotes.

In C#, strings are enclosed in double quotes. Single quotes are for characters.

2fill in blank

medium

Complete the code to concatenate two strings str1 and str2 using the + operator.

DSA C#

string result = str1 [1] str2;

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

A+

B*

C&

D++

Attempts:

3 left

💡 Hint

Common Mistakes

Using * or & instead of + for string concatenation.

Using ++ which is for incrementing numbers.

In C#, the + operator is used to join two strings together.

3fill in blank

hard

Fix the error in the code to get the length of the string named text.

DSA C#

int length = text[1];

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

A.length

B.Length

C.Length()

Dlength

Attempts:

3 left

💡 Hint

Common Mistakes

Using .Length() as if it were a method.

Using lowercase .length which is not valid in C#.

In C#, string length is accessed with the property .Length without parentheses.

4fill in blank

hard

Fill both blanks to check if the string input equals "yes" ignoring case.

DSA C#

bool isYes = input.[1]("yes", [2]);

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

AEquals

BCompareTo

CStringComparison.OrdinalIgnoreCase

DStringComparison.CurrentCulture

Attempts:

3 left

💡 Hint

Common Mistakes

Using CompareTo which does not take StringComparison parameter.

Using StringComparison.CurrentCulture which is case sensitive.

Use Equals method with StringComparison.OrdinalIgnoreCase to compare strings ignoring case.

5fill in blank

hard

Fill all three blanks to create a new string from original by replacing "cat" with "dog" and converting to uppercase.

DSA C#

string newStr = original.[1]("cat", "dog").[2]().[3]();

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

AReplace

BToUpper

CTrim

DToLower

Attempts:

3 left

💡 Hint

Common Mistakes

Using ToLower instead of ToUpper.

Calling Trim before Replace or ToUpper.

First replace "cat" with "dog", then convert to uppercase, then trim whitespace.

Practice

1. In C#, which of the following statements about strings is true?

easy

A. Strings are always stored in unmanaged memory.

B. Strings are mutable and can be changed directly after creation.

C. Strings are stored as arrays of characters that can be resized dynamically.

D. Strings are immutable, meaning once created, they cannot be changed.

Solution

1. Step 1: Understand string immutability in C#

   In C#, strings are immutable, so any change creates a new string object.

2. Step 2: Compare options with C# string behavior

   Strings are immutable, meaning once created, they cannot be changed. correctly states immutability; others describe behaviors not true for C# strings.

3. Final Answer:

   Strings are immutable, meaning once created, they cannot be changed. -> Option D

4. Quick Check:

   Immutable strings = Strings are immutable, meaning once created, they cannot be changed. [OK]

Hint: Remember: C# strings cannot be changed after creation [OK]

Common Mistakes:

• Thinking strings can be changed directly like arrays
• Confusing string mutability with StringBuilder
• Assuming strings are stored in unmanaged memory

2. Which of the following is the correct way to declare and initialize a string in C#?

easy

A. string s = "hello";

B. string s = 'hello';

C. string s = hello;

D. string s = new string(hello);

Solution

1. Step 1: Check string literal syntax in C#

   Strings must be enclosed in double quotes " ". Single quotes are for chars.

2. Step 2: Validate each option

   string s = "hello"; uses double quotes correctly. string s = 'hello'; uses single quotes (wrong). string s = hello; misses quotes. string s = new string(hello); syntax is invalid.

3. Final Answer:

   string s = "hello"; -> Option A

4. Quick Check:

   Double quotes for strings = string s = "hello"; [OK]

Hint: Use double quotes "" for strings in C# [OK]

Common Mistakes:

• Using single quotes for strings
• Forgetting quotes around string literals
• Trying to use new string() with a string literal

3. What is the output of the following C# code?

string s1 = "hello";
string s2 = s1;
s2 = "world";
Console.WriteLine(s1);

medium

A. world

B. hello

C. null

D. Compilation error

Solution

1. Step 1: Understand string assignment and immutability

   s2 initially points to the same string as s1. Changing s2 to "world" creates a new string object for s2.

2. Step 2: Check what s1 points to after s2 changes

   s1 still points to "hello" because strings are immutable and s2 reassignment does not affect s1.

3. Final Answer:

   hello -> Option B

4. Quick Check:

   Immutable strings keep original value = hello [OK]

Hint: Changing one string variable doesn't affect another [OK]

Common Mistakes:

• Assuming s1 changes when s2 is reassigned
• Confusing string references with mutable objects
• Expecting runtime or compile errors

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

string s = "hello";
s[0] = 'H';
Console.WriteLine(s);

medium

A. Cannot assign to s[0] because strings are immutable.

B. Missing semicolon after string declaration.

C. Character literals must be in double quotes.

D. Console.WriteLine cannot print strings.

Solution

1. Step 1: Check string mutability and indexing

   Strings in C# are immutable; you cannot change characters by index.

2. Step 2: Validate other options

   Semicolons are present, character literals use single quotes correctly, Console.WriteLine can print strings.

3. Final Answer:

   Cannot assign to s[0] because strings are immutable. -> Option A

4. Quick Check:

   Strings immutable = cannot change characters by index [OK]

Hint: Strings cannot be changed by index in C# [OK]

Common Mistakes:

• Trying to modify string characters directly
• Confusing char and string literal syntax
• Assuming Console.WriteLine can't print strings

5. Given the following C# code, what will be the output?

string s = "abc";
string t = s + "def";
string u = t.Replace('a', 'z');
Console.WriteLine(s);
Console.WriteLine(t);
Console.WriteLine(u);

hard

A. abc
def
zbcdef

B. abc
abcdef
abcdef

C. abc
abcdef
zbcdef

D. Compilation error due to Replace usage

Solution

1. Step 1: Analyze string concatenation

   t = s + "def" results in "abcdef".

2. Step 2: Analyze Replace method

   u = t.Replace('a', 'z') replaces 'a' with 'z' in "abcdef", resulting in "zbcdef".

3. Step 3: Check original strings remain unchanged

   s remains "abc" because strings are immutable.

4. Final Answer:

   abc abcdef zbcdef -> Option C

5. Quick Check:

   Immutable strings + Replace returns new string = abc abcdef zbcdef [OK]

Hint: Replace returns new string; originals stay same [OK]

Common Mistakes:

• Expecting Replace to change original string
• Confusing concatenation result
• Thinking Replace causes compile error