Operator precedence and evaluation order in C Sharp (C#) - Interactive Code Practice

Practice - 5 Tasks

1fill in blank

easy

Complete the code to correctly add 3 and 4, then multiply by 2.

C Sharp (C#)

int result = (3 + 4) [1] 2;
Console.WriteLine(result);

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

A/

B*

C-

D+

Attempts:

3 left

💡 Hint

Common Mistakes

Using + instead of * causes the result to be 9 instead of 14.

The multiplication operator (*) has higher precedence than addition, but parentheses force addition first. So (3 + 4) * 2 = 14.

2fill in blank

medium

Complete the code to check if 5 is greater than 3 and less than 10.

C Sharp (C#)

bool check = 5 [1] 3 && 5 < 10;
Console.WriteLine(check);

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

A>

B<

C==

D<=

Attempts:

3 left

💡 Hint

Common Mistakes

Using < instead of > reverses the logic and results in false.

The expression 5 > 3 checks if 5 is greater than 3, which is true. Combined with 5 < 10, the whole expression is true.

3fill in blank

hard

Fix the error in the expression to correctly compute the value.

C Sharp (C#)

int value = 10 + 5 [1] 2;
Console.WriteLine(value);

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

A/

B+

C-

D*

Attempts:

3 left

💡 Hint

Common Mistakes

Using + instead of * causes the result to be 17 instead of 20.

Multiplication (*) has higher precedence than addition, so 5 * 2 is calculated first, then added to 10, resulting in 20.

4fill in blank

hard

Fill both blanks to create a dictionary with word lengths for words longer than 3 characters.

C Sharp (C#)

var lengths = new Dictionary<string, int> {
    {"apple", "apple".Length},
    {"bat", "bat".Length}
};
var filtered = lengths.Where(kv => kv.Value [1] 3).ToDictionary(kv => kv.Key, kv => kv.Value [2] 1);
foreach(var item in filtered) Console.WriteLine($"{item.Key}: {item.Value}");

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

A>

B+

C-

D<

Attempts:

3 left

💡 Hint

Common Mistakes

Using < instead of > filters wrong words.

Using - instead of + decreases lengths incorrectly.

The filter keeps words with length greater than 3. Then it adds 1 to each length in the new dictionary.

5fill in blank

hard

Fill all three blanks to create a dictionary with uppercase keys and values greater than 0.

C Sharp (C#)

var data = new Dictionary<string, int> { {"a", 1}, {"b", 0}, {"c", 3} };
var result = data.Where(kv => kv.Value [1] 0).ToDictionary(kv => kv.Key.[2](), kv => kv.[3]);
foreach(var item in result) Console.WriteLine($"{item.Key}: {item.Value}");

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

A==

BValue

C>

DToUpper

Attempts:

3 left

💡 Hint

Common Mistakes

Using == filters only values equal to zero.

Using Key instead of Value for values causes errors.

The filter keeps entries with Value > 0. The keys are converted to uppercase using ToUpper(), and the values are kept as Value.

Practice

1. Which operator has the highest precedence in the expression 3 + 4 * 2?

easy

A. Subtraction (-)

B. Addition (+)

C. Division (/)

D. Multiplication (*)

Solution

1. Step 1: Recall operator precedence rules

   Multiplication (*) has higher precedence than addition (+) in C#.

2. Step 2: Apply precedence to the expression

   The multiplication 4 * 2 is evaluated first, then 3 is added.

3. Final Answer:

   Multiplication (*) -> Option D

4. Quick Check:

   Multiplication before addition = Multiplication (*) [OK]

Hint: Multiplication and division come before addition and subtraction [OK]

Common Mistakes:

• Thinking addition happens before multiplication
• Ignoring operator precedence
• Assuming left-to-right always applies

2. Which of the following expressions is correctly using parentheses to change the evaluation order in C#?

easy

A. int result = 3 + 4 * 2);

B. int result = (3 + 4 * 2;

C. int result = 3 + (4 * 2);

D. int result = 3 + 4 * 2;

Solution

1. Step 1: Check parentheses balance and syntax

   int result = 3 + (4 * 2); has balanced parentheses around (4 * 2), which is correct syntax.

2. Step 2: Verify other options for syntax errors

   Options A and C have unbalanced parentheses, and D has no parentheses to change order.

3. Final Answer:

   int result = 3 + (4 * 2); -> Option C

4. Quick Check:

   Balanced parentheses change order correctly [OK]

Hint: Parentheses must be balanced and properly placed [OK]

Common Mistakes:

• Leaving parentheses unbalanced
• Placing parentheses incorrectly
• Forgetting to close parentheses

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

int a = 5;
int b = 3;
int c = 2;
int result = a - b + c * 4;
Console.WriteLine(result);

medium

A. 10

B. 8

C. 6

D. 4

Solution

1. Step 1: Identify operator precedence in the expression

   Multiplication (*) has higher precedence than addition (+) and subtraction (-), so c * 4 is evaluated first: 2 * 4 = 8.

2. Step 2: Evaluate the remaining expression left to right

   Now compute a - b + 8: 5 - 3 = 2, then 2 + 8 = 10.

3. Final Answer:

   10 -> Option A

4. Quick Check:

   Multiplication before addition/subtraction [OK]

Hint: Multiply before add or subtract [OK]

Common Mistakes:

• Adding before multiplying
• Ignoring operator precedence
• Calculating left to right without precedence

4. Identify the error in the following C# code snippet:

int x = 10;
int y = 5;
int z = x / y * 2 +;
Console.WriteLine(z);

medium

A. Division operator '/' is invalid here

B. Missing operand after '+' operator

C. Variables x and y are not declared

D. Console.WriteLine syntax is incorrect

Solution

1. Step 1: Check the expression for syntax errors

   The expression ends with a '+' operator without a following operand, which is invalid syntax.

2. Step 2: Verify other parts of the code

   Variables x and y are declared correctly, division operator is valid, and Console.WriteLine syntax is correct.

3. Final Answer:

   Missing operand after '+' operator -> Option B

4. Quick Check:

   Operator must have operands on both sides [OK]

Hint: Check for missing operands near operators [OK]

Common Mistakes:

• Ignoring incomplete expressions
• Assuming division operator is wrong
• Overlooking missing semicolons

5. Given the code below, what is the value of result? Consider operator precedence and evaluation order.

int a = 2;
int b = 3;
int c = 4;
int result = a + b * c - (a + b) * c / b;

hard

A. 8

B. 4

C. 6

D. 2

Solution

1. Step 1: Evaluate expressions inside parentheses first

   (a + b) = 2 + 3 = 5.

2. Step 2: Calculate multiplication and division next

   b * c = 3 * 4 = 12.
   (a + b) * c / b = 5 * 4 / 3 = 20 / 3 = 6 (integer division truncates).

3. Step 3: Calculate the full expression left to right

   a + b * c - (a + b) * c / b = 2 + 12 - 6 = 14 - 6 = 8.

4. Step 4: Re-check integer division

   20 / 3 = 6 (integer division truncates decimals).

5. Final Answer:

   8 -> Option A

6. Quick Check:

   Parentheses first, then multiply/divide, then add/subtract [OK]

Hint: Parentheses first, then multiply/divide, then add/subtract [OK]

Common Mistakes:

• Ignoring integer division truncation
• Evaluating left to right without precedence
• Calculating parentheses last