String interpolation in C Sharp (C#) - Practice Problems & Coding Challenges

Challenge - 5 Problems

❓ Predict Output

intermediate

Output of simple string interpolation

What is the output of this C# code using string interpolation?

C Sharp (C#)

int apples = 5;
int oranges = 3;
string result = $"I have {apples} apples and {oranges} oranges.";
Console.WriteLine(result);

A I have 5 apples and 3 oranges.

B I have {apples} apples and {oranges} oranges.

C I have apples oranges.

D I have 8 apples and oranges.

💡 Hint

Look at how variables inside curly braces are replaced by their values.

The $ symbol before the string allows variables inside { } to be replaced by their values. So {apples} becomes 5 and {oranges} becomes 3.

❓ Predict Output

intermediate

Output with expression inside interpolation

What will this C# code print?

C Sharp (C#)

int x = 4;
int y = 7;
Console.WriteLine($"Sum is {x + y}");

A Sum is 47

B Sum is x + y

C Sum is {x + y}

D Sum is 11

💡 Hint

Inside { }, you can put expressions, not just variables.

The expression x + y is evaluated to 11 and inserted into the string.

❓ Predict Output

advanced

Output with format specifier in interpolation

What is the output of this C# code?

C Sharp (C#)

double price = 1234.5678;
Console.WriteLine($"Price: {price:F2}");

A Price: 1234.5678

B Price: 1234.57

C Price: {price:F2}

D Price: 1234.5

💡 Hint

The :F2 means format the number with 2 decimal places.

The format specifier F2 rounds the number to 2 decimal places.

❓ Predict Output

advanced

Output with nested interpolation and escape sequences

What will this C# code print?

C Sharp (C#)

string name = "Anna";
int age = 30;
Console.WriteLine($"Name: {name}, Age: {age}\nWelcome!");

A Name: Anna, Age: 30 Welcome!

B Name: Anna, Age: 30\nWelcome!

C

Name: Anna, Age: 30
Welcome!

D Name: {name}, Age: {age}\nWelcome!

💡 Hint

The \n is a newline character and will create a line break.

The \n creates a new line after Age: 30, so Welcome! appears on the next line.

🧠 Conceptual

expert

Understanding string interpolation with null values

What is the output of this C# code snippet?

C Sharp (C#)

string? city = null;
Console.WriteLine($"City: {city ?? "Unknown"}");

A City: Unknown

B City: {city ?? "Unknown"}

C City: null

D City:

💡 Hint

The ?? operator returns the right side if the left side is null.

Since city is null, the expression city ?? "Unknown" evaluates to "Unknown".

Practice

1. What does string interpolation in C# allow you to do?

easy

A. Use variables only outside of strings

B. Insert variables directly inside a string using { } with a $ prefix

C. Create strings without any variables

D. Concatenate strings using the + operator only

Solution

1. Step 1: Understand string interpolation syntax

   String interpolation uses a $ before the string and curly braces { } to insert variables inside the string.

2. Step 2: Compare options with this syntax

   Only Insert variables directly inside a string using { } with a $ prefix describes inserting variables inside strings using { } with a $ prefix.

3. Final Answer:

   Insert variables directly inside a string using { } with a $ prefix -> Option B

4. Quick Check:

   String interpolation = $ + {variable} [OK]

Hint: Look for $ and { } to spot string interpolation [OK]

Common Mistakes:

• Confusing concatenation (+) with interpolation
• Forgetting the $ before the string
• Using variables outside the string only

2. Which of the following is the correct syntax for string interpolation in C#?

easy

A. string message = $"Hello, {name}!";

B. string message = "Hello, {name}!";

C. string message = $'Hello, {name}!';

D. string message = 'Hello, {name}!';

Solution

1. Step 1: Identify correct string interpolation syntax

   In C#, string interpolation requires a $ before a double-quoted string and variables inside { }.

2. Step 2: Check each option

   string message = $"Hello, {name}!"; uses $ before double quotes and {name} inside, which is correct. The remaining options lack $ or use single quotes which is invalid for interpolation.

3. Final Answer:

   string message = $"Hello, {name}!"; -> Option A

4. Quick Check:

   $ + "string" + {variable} = correct syntax [OK]

Hint: Use $ before double quotes for interpolation [OK]

Common Mistakes:

• Using single quotes instead of double quotes
• Omitting the $ symbol
• Placing variables outside { }

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

int apples = 5;
int oranges = 3;
string result = $"I have {apples + oranges} fruits.";
Console.WriteLine(result);

medium

A. I have 8 fruits.

B. I have {apples + oranges} fruits.

C. I have apples + oranges fruits.

D. I have 53 fruits.

Solution

1. Step 1: Evaluate the expression inside the interpolation

   The expression {apples + oranges} adds 5 + 3, which equals 8.

2. Step 2: Substitute the result into the string

   The string becomes "I have 8 fruits." and is printed.

3. Final Answer:

   I have 8 fruits. -> Option A

4. Quick Check:

   Expression inside { } is calculated before output [OK]

Hint: Calculate expressions inside { } before printing [OK]

Common Mistakes:

• Printing the expression text instead of its value
• Concatenating numbers as strings incorrectly
• Ignoring the + operator inside { }

4. Identify the error in this code snippet:

int age = 30;
string message = $"Your age is {age";
Console.WriteLine(message);

medium

A. age variable is not declared

B. Missing $ before the string

C. Missing closing brace } in the interpolation

D. Console.WriteLine is misspelled

Solution

1. Step 1: Check the interpolation braces

   The string has an opening { but no closing } after age, causing a syntax error.

2. Step 2: Verify other parts

   The $ is present, age is declared, and Console.WriteLine is correct.

3. Final Answer:

   Missing closing brace } in the interpolation -> Option C

4. Quick Check:

   Every { must have a matching } [OK]

Hint: Count { and } to avoid missing braces [OK]

Common Mistakes:

• Forgetting to close interpolation braces
• Removing $ accidentally
• Assuming variable is undeclared without checking

5. You want to display a price with two decimal places using string interpolation. Which code correctly formats the price variable?

double price = 12.5;
// Fill in the blank:
string output = $"Price: {___}";
Console.WriteLine(output);

hard

A. price:.2

B. price.ToFixed(2)

C. "{price:2}"

D. price:F2

Solution

1. Step 1: Understand C# string interpolation formatting

   Inside { }, you can add :F2 to format a number with 2 decimals.

2. Step 2: Check each option

   price:F2 uses {price:F2} which is correct. price:.2 is an invalid format specifier (requires :F2 for fixed decimals). price.ToFixed(2) uses ToFixed which is JavaScript, not C#. "{price:2}" is invalid syntax.

3. Final Answer:

   price:F2 -> Option D

4. Quick Check:

   Use :F2 inside { } to format decimals [OK]

Hint: Use :F2 inside { } to show 2 decimals [OK]

Common Mistakes:

• Using JavaScript methods like ToFixed in C#
• Trying to format outside the interpolation braces
• Incorrect format string syntax