String Basics and Memory Representation in DSA C# - Interactive Practice

Practice - 5 Tasks

1fill in blank

easy

Complete the code to get the length of the string.

DSA C#

string text = "hello";
int length = text.[1];

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

ASize

BCount

CLength

DLength()

Attempts:

3 left

💡 Hint

Common Mistakes

Using Length() as if it were a method.

Using Count which is for collections, not strings.

The Length property returns the number of characters in the string.

2fill in blank

medium

Complete the code to get the first character of the string.

DSA C#

string word = "apple";
char firstChar = word[1]0;

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

A.

B{

C(

D[

Attempts:

3 left

💡 Hint

Common Mistakes

Using dot notation instead of brackets to access characters.

Using parentheses which are for methods.

Strings can be accessed like arrays using square brackets [] with the index inside.

3fill in blank

hard

Fix the error in the code to convert the string to uppercase.

DSA C#

string name = "john";
string upperName = name.[1]();

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

AToUpper

Btoupper

CToUpperCase

DUpperCase

Attempts:

3 left

💡 Hint

Common Mistakes

Using lowercase or incorrect method names.

Forgetting the parentheses to call the method.

The correct method to convert a string to uppercase in C# is ToUpper().

4fill in blank

hard

Fill both blanks to create a substring from index 2 with length 3.

DSA C#

string text = "example";
string sub = text.[1]([2], 3);

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

ASubstring

BSubstr

C2

D3

Attempts:

3 left

💡 Hint

Common Mistakes

Using 'Substr' which is not a C# method.

Confusing the order of arguments.

The Substring method extracts a part of the string starting at the given index. Here, index 2 and length 3 are used.

5fill in blank

hard

Fill all three blanks to check if the string contains 'cat' and print a message.

DSA C#

string animal = "concatenate";
if (animal.[1]("[2]"))
{
    Console.[3]("Found cat!");
}

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

AContains

Bcat

CWriteLine

DIndexOf

Attempts:

3 left

💡 Hint

Common Mistakes

Using IndexOf without comparing the result.

Using incorrect method names or missing quotes around the substring.

The Contains method checks if a substring exists inside a string. WriteLine prints the message to the console.

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