String type and immutability in C Sharp (C#) - Practice Problems & Coding Challenges

Challenge - 5 Problems

❓ Predict Output

intermediate

What is the output of this code?

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

C Sharp (C#)

string s = "hello";
s = s.Replace('h', 'j');
Console.WriteLine(s);

A Hello

B jello

C hello

D jello\nhello

💡 Hint

Remember that strings in C# are immutable. The Replace method returns a new string but does not change the original.

The Replace method returns a new string with the replacements, but since the returned value is not assigned, the original string 's' remains unchanged. So, 'hello' is printed.

❓ Predict Output

intermediate

What is the output of this code?

What will this C# program print?

C Sharp (C#)

string a = "abc";
string b = a + "def";
Console.WriteLine(a);
Console.WriteLine(b);

A abcdef\nabc

B abcdef\nabcdef

C abc\nabc

D abc\nabcdef

💡 Hint

Adding strings creates a new string; the original string remains unchanged.

The variable 'a' remains 'abc'. The variable 'b' is a new string 'abcdef'. So the output is 'abc' then 'abcdef'.

🔧 Debug

advanced

Why does this code not change the string?

This code tries to change the first character of a string. Why does it fail?

C Sharp (C#)

string s = "test";
s[0] = 'b';
Console.WriteLine(s);

A Compilation error: strings are immutable and cannot be changed by index.

B Runtime error: index out of range.

C Output: test

D Output: best

💡 Hint

Think about whether you can assign to a character in a string by index in C#.

Strings in C# are immutable. You cannot assign to an index of a string. This causes a compilation error.

❓ Predict Output

advanced

What is the output of this code?

What will this program print?

C Sharp (C#)

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

A HELLO\nHELLO

B hello\nHELLO

C hello\nhello

D HELLO\nhello

💡 Hint

ToUpper returns a new string; it does not change the original string.

s1 remains 'hello' because strings are immutable. s2 is a new string 'HELLO'.

🧠 Conceptual

expert

Why is string immutability important in C#?

Which of the following is NOT a reason why strings are immutable in C#?

A It allows direct modification of characters in the string to save memory.

B It improves performance by enabling string interning and caching.

C It allows strings to be safely shared across multiple threads without synchronization.

D It simplifies security by preventing unexpected changes to string data.

💡 Hint

Think about what immutability means and how it affects string modification.

Strings being immutable means you cannot modify characters directly. This is a design choice for safety and performance, not to allow direct modification.