Assignment and compound assignment in C Sharp (C#) - Cheat Sheet & Quick Revision

Recall & Review

beginner

What is the purpose of the assignment operator = in C#?

The assignment operator = is used to store a value into a variable. It takes the value on the right and puts it into the variable on the left.

beginner

What does the compound assignment operator += do?

The += operator adds the value on the right to the variable on the left and then stores the result back into that variable. It's a shortcut for variable = variable + value.

beginner

Explain the difference between = and += operators.

= assigns a new value to a variable, replacing the old one. += adds a value to the current value of the variable and updates it with the sum.

beginner

Given int x = 5; what is the value of x after x *= 3;?

The value of x becomes 15 because x *= 3 multiplies x by 3 and assigns the result back to x.

beginner

Can compound assignment operators be used with strings in C#? For example, str += "hello";

Yes, the += operator can be used to append strings. It adds the right string to the end of the left string and stores the result.

What does the statement count -= 2; do?

A Subtracts 2 from count and updates count

B Assigns 2 to count

C Adds 2 to count

D Multiplies count by 2

The -= operator subtracts the value on the right from the variable on the left and updates it.

Which operator is equivalent to number = number / 4;?

A number += 4;

B number /= 4;

C number *= 4;

D number -= 4;

The /= operator divides the variable by the value and assigns the result back.

What is the value of total after total = 10; total += 5;?

A 15

B 10

C 5

D 50

The += operator adds 5 to 10, so total becomes 15.

Which of these is NOT a compound assignment operator in C#?

A +=

B -=

C *=

D ==

== is a comparison operator, not an assignment operator.

If str = "Hi";, what does str += " there"; do?

A Replaces str with " there"

B Deletes str

C Appends " there" to str

D Throws an error

The += operator appends the string on the right to the existing string.

Explain how compound assignment operators simplify code compared to using regular assignment.

Think about how you can do math and assignment in one step.

List at least three compound assignment operators in C# and describe what each does.

Remember operators that combine math with assignment.

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