Comparison operators in C Sharp (C#) - Cheat Sheet & Quick Revision

Recall & Review

beginner

What does the '==' operator do in C#?

The '==' operator checks if two values are equal. It returns true if they are the same, and false if they are different.

beginner

What is the difference between '==' and '!=' operators?

'==' checks if two values are equal, while '!=' checks if two values are not equal.

beginner

List the four main comparison operators for ordering in C#.

The four main ordering comparison operators are: '<' (less than), '>' (greater than), '<=' (less than or equal to), '>=' (greater than or equal to).

beginner

What type of value do comparison operators return?

Comparison operators return a boolean value: true or false.

intermediate

Can comparison operators be used with strings in C#? If yes, how?

Yes, comparison operators like '==' and '!=' can be used to check if two strings are equal or not. For ordering comparisons, use methods like String.Compare.

What does the expression (5 > 3) evaluate to in C#?

A 3

B false

C 5

D true

5 is greater than 3, so (5 > 3) evaluates to true.

Which operator checks if two values are not equal?

A ==

B <=

C !=

D >=

'!=' checks if two values are not equal.

What is the result type of a comparison operation in C#?

A bool

B string

C int

D double

Comparison operators return a boolean (bool) value: true or false.

Which operator means 'less than or equal to'?

A <

B <=

C >

D >=

'<=' means less than or equal to.

Can you use '>' operator to compare two strings directly in C#?

A No, you must use String.Compare method

B Yes, it compares alphabetically

C Yes, but only for string length

D No, strings cannot be compared

You cannot use '>' directly on strings; use String.Compare for ordering comparisons.

Explain how comparison operators work in C# and give examples of their use.

Think about how you check if two things are equal or one is bigger.

Describe the difference between equality and ordering comparison operators in C#.

Consider checking if things are the same versus which is bigger or smaller.

Practice

1. Which of the following comparison operators checks if two values are equal in C#?

easy

A. >

B. =

C. !=

D. ==

Solution

1. Step 1: Understand the equality operator

   The operator == is used to check if two values are equal in C#.

2. Step 2: Differentiate from assignment and other operators

   = is for assignment, != checks inequality, and > checks if left is greater than right.

3. Final Answer:

   == -> Option D

4. Quick Check:

   Equality operator = == [OK]

Hint: Use double equals (==) to check equality, not single equals [OK]

Common Mistakes:

• Using single equals (=) instead of double equals (==)
• Confusing != with == operator
• Using > when checking equality

2. Which of the following is the correct syntax to check if variable x is not equal to 10 in C#?

easy

A. if (x != 10)

B. if (x =! 10)

C. if (x = 10)

D. if (x ==! 10)

Solution

1. Step 1: Identify the correct not equal operator

   The operator != is used to check if two values are not equal in C#.

2. Step 2: Check syntax correctness

   if (x != 10) is correct syntax. The others have incorrect operator placement or use assignment instead of comparison.

3. Final Answer:

   if (x != 10) -> Option A

4. Quick Check:

   Not equal operator = != [OK]

Hint: Use != to check not equal, watch operator order carefully [OK]

Common Mistakes:

• Writing =! instead of != operator
• Using single = instead of comparison operator
• Combining == and ! incorrectly

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

int a = 5;
int b = 8;
Console.WriteLine(a > b);

medium

A. 5

B. True

C. False

D. 8

Solution

1. Step 1: Compare values of a and b

   Variable a is 5 and b is 8. The expression a > b checks if 5 is greater than 8.

2. Step 2: Evaluate the comparison

   Since 5 is not greater than 8, the expression returns false.

3. Final Answer:

   False -> Option C

4. Quick Check:

   5 > 8 = False [OK]

Hint: Compare values carefully; 5 is not greater than 8 [OK]

Common Mistakes:

• Assuming 5 > 8 is true
• Confusing output with variable values
• Expecting numeric output instead of boolean

4. Find the error in this C# code snippet:

int x = 10;
if (x = 5)
{
    Console.WriteLine("Equal");
}

medium

A. Using assignment (=) instead of comparison (==) in if condition

B. Missing semicolon after if statement

C. Incorrect variable declaration

D. Console.WriteLine syntax error

Solution

1. Step 1: Check the if condition syntax

   The condition uses = which assigns 5 to x instead of comparing.

2. Step 2: Correct operator usage

   Use == to compare values in conditions, so it should be if (x == 5).

3. Final Answer:

   Using assignment (=) instead of comparison (==) in if condition -> Option A

4. Quick Check:

   Comparison needs ==, not = [OK]

Hint: Use double equals (==) in conditions, not single equals (=) [OK]

Common Mistakes:

• Using = instead of == in if conditions
• Forgetting to use parentheses in if
• Misunderstanding assignment vs comparison

5. You want to check if a number n is between 10 and 20 inclusive in C#. Which condition correctly uses comparison operators?

hard

A. if (n > 10 || n < 20)

B. if (n >= 10 && n <= 20)

C. if (10 <= n <= 20)

D. if (n == 10 && n == 20)

Solution

1. Step 1: Understand range checking in C#

   C# does not support chained comparisons like 10 <= n <= 20. You must combine two comparisons with logical AND.

2. Step 2: Analyze each option

   if (n >= 10 && n <= 20) uses n >= 10 && n <= 20, which correctly checks if n is between 10 and 20 inclusive. if (10 <= n <= 20) is invalid syntax. if (n > 10 || n < 20) uses OR which is incorrect for range. if (n == 10 && n == 20) checks if n equals both 10 and 20 simultaneously, which is impossible.

3. Final Answer:

   if (n >= 10 && n <= 20) -> Option B

4. Quick Check:

   Use && to combine comparisons for ranges [OK]

Hint: Use && to combine two comparisons for range checks [OK]

Common Mistakes:

• Trying chained comparisons like 10 <= n <= 20
• Using || instead of && for range
• Checking impossible conditions with == for both ends