Assignment and compound assignment in C Sharp (C#) - Practice Problems & Coding Challenges

Challenge - 5 Problems

❓ Predict Output

intermediate

Output of compound assignment with strings

What is the output of this C# code snippet?

C Sharp (C#)

string s = "Hi";
s += " there";
Console.WriteLine(s);

A Hi there

B Hi

C there

D Hi+ there

💡 Hint

The += operator adds the right string to the left string.

The += operator appends the string on the right to the string on the left, so s becomes "Hi there".

❓ Predict Output

intermediate

Value after compound assignment with integers

What is the value of x after running this code?

C Sharp (C#)

int x = 5;
x *= 3 + 2;
Console.WriteLine(x);

A 10

B 15

C 25

D 30

💡 Hint

Remember operator precedence: multiplication and addition.

The expression x *= 3 + 2 is evaluated as x *= (3 + 2), so x = 5 * 5 = 25.

❓ Predict Output

advanced

Output of compound assignment with mixed types

What is the output of this code?

C Sharp (C#)

double d = 4.5;
int i = 2;
d /= i;
Console.WriteLine(d);

A 2

B 2.25

C 2.5

D Syntax error

💡 Hint

Division between double and int results in double.

d /= i divides d by i, so 4.5 / 2 = 2.25.

❓ Predict Output

advanced

Effect of compound assignment on boolean variables

What error or output does this code produce?

C Sharp (C#)

bool flag = true;
flag += false;
Console.WriteLine(flag);

A Compilation error

B True

C False

D Runtime error

💡 Hint

Can you add booleans with += in C#?

The += operator is not defined for bool types, so this causes a compilation error.

🧠 Conceptual

expert

Understanding compound assignment with nullable types

Given the code below, what is the value of n after execution?

C Sharp (C#)

int? n = null;
n ??= 10;
n += 5;
Console.WriteLine(n);

A Compilation error

B 5

C null

D 15

💡 Hint

The ??= operator assigns only if the variable is null.

n starts as null, so n ??= 10 sets n to 10. Then n += 5 adds 5, so n becomes 15.

Practice

1. What does the compound assignment operator += do in C#?

easy

A. Multiplies the left variable by the right value

B. Subtracts the right value from the left variable

C. Adds the right value to the left variable and assigns the result to the left variable

D. Divides the left variable by the right value

Solution

1. Step 1: Understand the operator meaning

   The += operator adds the right side value to the left side variable.

2. Step 2: Assign the result back

   The result of the addition is stored back into the left variable.

3. Final Answer:

   Adds the right value to the left variable and assigns the result to the left variable -> Option C

4. Quick Check:

   += means add and assign [OK]

Hint: Remember: += means add then assign in one step [OK]

Common Mistakes:

• Confusing += with subtraction or multiplication
• Thinking += just adds without assignment
• Using += on constants (which is invalid)

2. Which of the following is the correct syntax to multiply a variable x by 5 using a compound assignment in C#?

easy

A. x *= 5;

B. x =* 5;

C. x = *5;

D. x = x *=

Solution

1. Step 1: Identify correct compound assignment syntax

   The correct syntax for multiplication assignment is x *= 5; with no spaces between * and =.

2. Step 2: Check other options for syntax errors

   Options B, C, and D have invalid syntax or misplaced operators.

3. Final Answer:

   x *= 5; -> Option A

4. Quick Check:

   Use *= for multiply and assign [OK]

Hint: Compound operators combine symbol and = without spaces [OK]

Common Mistakes:

• Writing =* instead of *=
• Adding spaces between * and =
• Using incomplete or invalid syntax

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

int a = 10;
a += 5;
a -= 3;
Console.WriteLine(a);

medium

A. 12

B. 15

C. 8

D. 10

Solution

1. Step 1: Apply the first compound assignment

   Starting with a = 10, a += 5 adds 5, so a = 15.

2. Step 2: Apply the second compound assignment

   Then a -= 3 subtracts 3, so a = 12.

3. Final Answer:

   12 -> Option A

4. Quick Check:

   10 + 5 - 3 = 12 [OK]

Hint: Follow each compound step in order to find final value [OK]

Common Mistakes:

• Adding and subtracting in wrong order
• Confusing += and -= effects
• Forgetting to update variable after each step

4. Identify the error in the following code snippet:

int count = 5;
count + = 3;
Console.WriteLine(count);

medium

A. The variable count is not initialized

B. The code will output 8 without errors

C. Console.WriteLine is missing parentheses

D. The compound assignment operator has a space and is invalid

Solution

1. Step 1: Check variable initialization

   The variable count is correctly initialized to 5, so no error here.

2. Step 2: Examine the compound assignment syntax

   The code uses count + = 3; which has a space between + and =, making it invalid syntax. It should be count += 3;.

3. Final Answer:

   The compound assignment operator has a space and is invalid -> Option D

4. Quick Check:

   No spaces in compound operators like += [OK]

Hint: Compound operators must be written without spaces [OK]

Common Mistakes:

• Adding spaces between operator and =
• Assuming code runs despite syntax errors
• Confusing initialization errors with syntax errors

5. Given the code below, what will be the value of result after execution?

int x = 4;
int y = 3;
int result = 10;
result += x * y;
result -= y + 2;
result *= 2;

hard

A. 30

B. 34

C. 26

D. 28

Solution

1. Step 1: Calculate result += x * y

   Multiply x * y = 4 * 3 = 12. Add to result = 10 + 12 = 22.

2. Step 2: Calculate result -= y + 2

   Add y + 2 = 3 + 2 = 5. Subtract from result = 22 - 5 = 17.

3. Step 3: Calculate result *= 2

   Multiply result = 17 * 2 = 34.

4. Final Answer:

   34 -> Option B

5. Quick Check:

   10 + 12 - 5 = 17; 17 * 2 = 34 [OK]

Hint: Perform operations step-by-step respecting operator precedence [OK]

Common Mistakes:

• Ignoring multiplication precedence in compound assignment
• Calculating additions/subtractions in wrong order
• Forgetting to update result after each step