How Strings Work Differently Across Languages in DSA C# - Debugging & Practice

Challenge - 5 Problems

❓ Predict Output

intermediate

What is the output of this C# string manipulation?

Consider the following C# code snippet. What will be printed to the console?

DSA C#

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

A "hello"

B "world"

C "hello world"

D null

💡 Hint

Remember that strings in C# are immutable and assignments copy references.

In C#, strings are immutable and variables hold references to string objects. When s2 = s1 is done, both point to "hello". Changing s1 to "world" makes s1 point to a new string, but s2 still points to "hello".

❓ Predict Output

intermediate

What does this JavaScript string code output?

Look at this JavaScript code. What will it print?

DSA C#

let s1 = "hello";
let s2 = s1;
s1 = "world";
console.log(s2);

A undefined

B "world"

C "hello"

D "hello world"

💡 Hint

Strings in JavaScript are immutable and variables hold references to string values.

JavaScript strings are immutable. Assigning s2 = s1 copies the reference to the string "hello". Changing s1 to "world" does not affect s2.

❓ Predict Output

advanced

What is the output of this Python string code?

What will this Python code print?

DSA C#

s1 = "hello"
s2 = s1
s1 = "world"
print(s2)

A "hello world"

B None

C "world"

D "hello"

💡 Hint

Python strings are immutable and variables hold references to string objects.

In Python, strings are immutable. Assigning s2 = s1 makes both variables point to the same string "hello". Changing s1 to "world" points s1 to a new string, but s2 remains "hello".

❓ Predict Output

advanced

What happens when modifying a string in Java?

What will this Java code print?

DSA C#

String s1 = "hello";
String s2 = s1;
s1 = "world";
System.out.println(s2);

A "hello"

B "world"

C "hello world"

D null

💡 Hint

Java strings are immutable and variables hold references to string objects.

Java strings are immutable. Assigning s2 = s1 makes both variables point to "hello". Changing s1 to "world" points s1 to a new string, but s2 still points to "hello".

🧠 Conceptual

expert

Why are strings immutable in many languages?

Which of the following is the main reason many programming languages make strings immutable?

A To make strings faster to modify in place

B To allow strings to be safely shared and reused without unexpected changes

C To prevent strings from being used as keys in dictionaries or maps

D To reduce the memory used by strings by compressing them automatically

💡 Hint

Think about safety and sharing of data in programs.

Immutability allows strings to be shared safely across different parts of a program without risk of one part changing the string unexpectedly for others. This helps with thread safety and caching.

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