String concatenation behavior in C Sharp (C#) - Interactive Code Practice

Practice - 5 Tasks

1fill in blank

easy

Complete the code to concatenate two strings and print the result.

C Sharp (C#)

string greeting = "Hello" + [1];
Console.WriteLine(greeting);

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

A" World"

BWorld

C' World'

D "World"

Attempts:

3 left

💡 Hint

Common Mistakes

Using single quotes instead of double quotes for strings.

Forgetting to put quotes around the string to concatenate.

In C#, strings must be enclosed in double quotes. Adding " World" concatenates the two strings correctly.

2fill in blank

medium

Complete the code to concatenate a string and an integer by converting the integer to a string.

C Sharp (C#)

int number = 5;
string message = "Number: " + [1];
Console.WriteLine(message);

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

AConvert.ToInt32(number)

Bnumber

Cnumber.ToString()

Dnumber + 1

Attempts:

3 left

💡 Hint

Common Mistakes

Trying to concatenate integer directly without conversion.

Using incorrect conversion methods like Convert.ToInt32 which converts to int, not string.

To concatenate an integer with a string, convert the integer to a string using ToString().

3fill in blank

hard

Fix the error in the code to concatenate strings using the String.Concat method.

C Sharp (C#)

string part1 = "Good";
string part2 = "Morning";
string result = String.Concat(part1, [1]);
Console.WriteLine(result);

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

Apart2

B"part2"

Cpart2.ToString()

Dpart1 + part2

Attempts:

3 left

💡 Hint

Common Mistakes

Using quotes around variable names, which makes them string literals.

Trying to concatenate inside the method call incorrectly.

The String.Concat method concatenates string arguments. Use the variable part2 directly without quotes.

4fill in blank

hard

Fill both blanks to create a string interpolation that includes a variable and an expression.

C Sharp (C#)

int apples = 3;
string message = $"I have [1] apples and [2] more.";
Console.WriteLine(message);

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

Aapples

Bapples + 2

C{apples + 2}

D{apples}

Attempts:

3 left

💡 Hint

Common Mistakes

Not using curly braces inside the interpolated string.

Using variables without braces in an interpolated string.

In string interpolation, expressions must be inside curly braces. Use {apples} and {apples + 2} inside the string.

5fill in blank

hard

Fill all three blanks to build a concatenated string with a variable, a method call, and a literal.

C Sharp (C#)

string name = "Anna";
string greeting = "Hello, " + [1] + ", you have " + [2] + [3];
Console.WriteLine(greeting);

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

Aname

Bname.ToUpper()

C" apples."

D" apples"

Attempts:

3 left

💡 Hint

Common Mistakes

Using quotes around variable names.

Forgetting the period in the string literal.

Not calling the method correctly.

The code concatenates the variable name, the uppercase version of name, and a string literal with a period. Use name, name.ToUpper(), and " apples.".

Practice

1. What does the + operator do when used between two strings in C#?

easy

A. It multiplies the two strings.

B. It subtracts the second string from the first.

C. It joins the two strings into one longer string.

D. It compares the two strings for equality.

Solution

1. Step 1: Understand the + operator with strings

   In C#, the + operator combines two strings by joining them end to end.

2. Step 2: Check other options

   Subtracting, multiplying, or comparing strings are not done with +. Those operations use other operators or methods.

3. Final Answer:

   It joins the two strings into one longer string. -> Option C

4. Quick Check:

   String + String = Joined String [OK]

Hint: Remember: + joins strings like glue [OK]

Common Mistakes:

• Thinking + subtracts or multiplies strings
• Confusing + with comparison operators
• Assuming + works only with numbers

2. Which of the following is the correct syntax to concatenate two strings str1 and str2 in C#?

easy

A. string result = str1 * str2;

B. string result = str1 + str2;

C. string result = str1 - str2;

D. string result = str1 / str2;

Solution

1. Step 1: Identify valid operators for string concatenation

   The + operator is used to join strings in C#. Other arithmetic operators like -, *, / are invalid for strings.

2. Step 2: Confirm syntax correctness

   The statement string result = str1 + str2; correctly concatenates and assigns the result.

3. Final Answer:

   string result = str1 + str2; -> Option B

4. Quick Check:

   Use + for string join [OK]

Hint: Use + to join strings, not arithmetic signs [OK]

Common Mistakes:

• Using - or * instead of + for strings
• Missing semicolon at end
• Trying to divide or multiply strings

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

string a = "Hello";
string b = "World";
string c = a + ", " + b + "!";
Console.WriteLine(c);

medium

A. Hello, World!

B. Hello World!

C. Hello,World!

D. HelloWorld!

Solution

1. Step 1: Analyze string concatenation parts

   The code joins "Hello", ", ", "World", and "!" in order, so the result is "Hello, World!".

2. Step 2: Confirm output of Console.WriteLine

   Console.WriteLine prints the combined string exactly as concatenated.

3. Final Answer:

   Hello, World! -> Option A

4. Quick Check:

   Strings + punctuation join as typed [OK]

Hint: Watch spaces and punctuation in concatenation [OK]

Common Mistakes:

• Missing spaces or commas in output
• Ignoring punctuation strings
• Confusing concatenation order

4. Identify the error in this code snippet:

string first = "Good";
string second = "Morning";
string message = first + second;
message += 5;
Console.WriteLine(message);

medium

A. Missing space between first and second strings.

B. Cannot add integer 5 to a string using += operator.

C. Variable 'message' is not declared.

D. Console.WriteLine syntax is incorrect.

Solution

1. Step 1: Check string concatenation and += usage

   The code concatenates "Good" and "Morning" without space, so message becomes "GoodMorning". Adding 5 converts 5 to string "5" and appends it, resulting in "GoodMorning5".

2. Step 2: Identify the main issue

   The code runs without error, but the missing space between words is a logical mistake causing output to look wrong.

3. Final Answer:

   Missing space between first and second strings. -> Option A

4. Quick Check:

   Check spaces when joining strings [OK]

Hint: Add spaces explicitly when joining words [OK]

Common Mistakes:

• Assuming += 5 causes error
• Ignoring missing spaces in output
• Thinking Console.WriteLine is wrong

5. Given a list of words string[] words = {"apple", "banana", "cherry"};, which code correctly concatenates them into a single comma-separated string using string.Concat?

hard

A. string result = string.Concat(words + ",");

B. string result = string.Concat(words[0] + words[1] + words[2]);

C. string result = string.Concat(words);

D. string result = string.Concat(words[0], ",", words[1], ",", words[2]);

Solution

1. Step 1: Understand string.Concat usage

   string.Concat can join multiple strings passed as arguments. To add commas, they must be separate arguments.

2. Step 2: Analyze each option

   string result = string.Concat(words[0], ",", words[1], ",", words[2]); passes each word and commas separately, correctly joining as "apple,banana,cherry". string result = string.Concat(words + ","); tries to add comma to array, invalid. string result = string.Concat(words); joins words without commas. string result = string.Concat(words[0] + words[1] + words[2]); concatenates words without commas inside Concat.

3. Final Answer:

   string result = string.Concat(words[0], ",", words[1], ",", words[2]); -> Option D

4. Quick Check:

   Pass each string and separator separately to Concat [OK]

Hint: Pass each string and comma separately to string.Concat [OK]

Common Mistakes:

• Trying to add commas inside array
• Passing array directly to Concat without separators
• Using + inside Concat argument incorrectly