String Basics and Memory Representation in DSA C# - Practice Problems & Challenges

Challenge - 5 Problems

❓ Predict Output

intermediate

What is the output of this C# string code?

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

DSA C#

string s1 = "hello";
string s2 = "hello";
Console.WriteLine(object.ReferenceEquals(s1, s2));

A True

B False

C hello

D Compilation error

💡 Hint

Think about how C# handles string literals in memory.

In C#, string literals are interned, meaning identical literals share the same memory reference. So, s1 and s2 point to the same object, making ReferenceEquals return True.

❓ Predict Output

intermediate

What is the output after modifying a string variable?

What will be printed by this C# code?

DSA C#

string s = "abc";
s = s + "d";
Console.WriteLine(s);

A d

B abc

C abcd

D Compilation error

💡 Hint

Remember strings are immutable but concatenation creates a new string.

Strings in C# are immutable, so concatenation creates a new string "abcd" and assigns it to s. The output is "abcd".

🔧 Debug

advanced

What error does this code raise?

What error will this C# code produce when run?

DSA C#

string s = null;
int length = s.Length;
Console.WriteLine(length);

A 0

B Compilation error

C IndexOutOfRangeException

D NullReferenceException

💡 Hint

Accessing a member on a null object causes an error.

Since s is null, accessing s.Length throws a NullReferenceException at runtime.

🧠 Conceptual

advanced

How many objects are created in memory?

How many string objects are created in memory after this code runs?

DSA C#

string a = "cat";
string b = "cat";
string c = new string(new char[] {'c','a','t'});

A 2

B 1

C 3

D 4

💡 Hint

Consider string interning and the new string constructor.

"cat" literal is interned once, so a and b point to the same object. The new string created by c is a separate object. Total 2 objects.

🚀 Application

expert

What is the output of this string manipulation code?

What will be printed by this C# code snippet?

DSA C#

string s = "hello";
char[] arr = s.ToCharArray();
arr[0] = 'j';
string s2 = new string(arr);
Console.WriteLine(s);
Console.WriteLine(s2);

A

jello
jello

B

hello
jello

C

hello
hello

D Compilation error

💡 Hint

Strings are immutable; modifying the char array does not change the original string.

The original string s remains "hello". The char array is modified and used to create s2 as "jello".

Practice

1. What does the string type in C# represent in memory?

easy

A. A list of integers representing ASCII codes

B. A sequence of characters stored as Unicode values

C. A mutable array of bytes

D. A pointer to a memory address without data

Solution

1. Step 1: Understand string storage in C#

   C# strings store characters as Unicode, allowing international text.

2. Step 2: Compare options with string behavior

   Only A sequence of characters stored as Unicode values correctly describes strings as sequences of Unicode characters.

3. Final Answer:

   A sequence of characters stored as Unicode values -> Option B

4. Quick Check:

   string = Unicode characters [OK]

Hint: Remember C# strings are Unicode sequences, not byte arrays [OK]

Common Mistakes:

• Thinking strings are mutable arrays
• Confusing ASCII with Unicode
• Assuming strings are just pointers

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 = "hello";
char[] arr = s;

Solution

1. Step 1: Check string literal syntax

   In C#, string literals use double quotes, so "hello" is correct.

2. Step 2: Validate each option

   string s = 'hello'; uses single quotes (for chars), B misses quotes, D tries to assign string to char array directly (invalid).

3. Final Answer:

   string s = "hello"; -> Option A

4. Quick Check:

   Strings use double quotes in C# [OK]

Hint: Use double quotes for strings, single quotes for chars [OK]

Common Mistakes:

• Using single quotes for strings
• Forgetting quotes around text
• Assigning string directly to char array

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

string s1 = "hello";
string s2 = "hello";
Console.WriteLine(object.ReferenceEquals(s1, s2));

medium

A. true

B. false

C. Compilation error

D. Runtime exception

Solution

1. Step 1: Understand string interning in C#

   String literals with same content are interned and share the same reference.

2. Step 2: Check ReferenceEquals for s1 and s2

   Since both are "hello" literals, ReferenceEquals returns true.

3. Final Answer:

   true -> Option A

4. Quick Check:

   String literals share references = true [OK]

Hint: String literals with same text share references [OK]

Common Mistakes:

• Assuming ReferenceEquals returns false for equal strings
• Confusing value equality with reference equality
• Expecting runtime errors

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

string s = "test";
s[0] = 'T';
Console.WriteLine(s);

medium

A. Runtime error: index out of range

B. Syntax error: missing semicolon

C. Strings are immutable; cannot assign to s[0]

D. No error; output is "Test"

Solution

1. Step 1: Check string mutability in C#

   Strings are immutable; individual characters cannot be changed by index.

2. Step 2: Analyze assignment to s[0]

   Assigning to s[0] causes a compile-time error because strings cannot be modified this way.

3. Final Answer:

   Strings are immutable; cannot assign to s[0] -> Option C

4. Quick Check:

   Strings immutable = assignment error [OK]

Hint: Remember strings cannot be changed character-by-character [OK]

Common Mistakes:

• Trying to modify string characters directly
• Expecting runtime error instead of compile error
• Assuming strings behave like char arrays

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

string s = "hello";
string t = s + " world";
Console.WriteLine(s);
Console.WriteLine(t);

Choose the correct output representation.

hard

A. hello world
hello

B. hello world
hello world

C. hello
world

D. hello
hello world

Solution

1. Step 1: Understand string concatenation and immutability

   Concatenation creates a new string; original string s remains unchanged.

2. Step 2: Trace the output statements

   Console.WriteLine(s) prints hello; Console.WriteLine(t) prints hello world.

3. Final Answer:

   hello hello world -> Option D

4. Quick Check:

   Original string unchanged, new string created [OK]

Hint: Concatenation creates new string; original stays same [OK]

Common Mistakes:

• Assuming original string changes after concatenation
• Mixing order of printed strings
• Confusing string references with values