Relational operators in C++ - Cheat Sheet & Quick Revision

Recall & Review

beginner

What are relational operators in C++?

Relational operators compare two values and return true or false depending on the comparison result.

beginner

List the six common relational operators in C++.

The six common relational operators are:
1. == (equal to)
2. != (not equal to)
3. < (less than)
4. > (greater than)
5. <= (less than or equal to)
6. >= (greater than or equal to)

beginner

What is the output of this code?

int a = 5, b = 10;
std::cout << (a < b);

The output is 1 because 5 is less than 10, so the expression a < b is true. In C++, true prints as 1.

beginner

How do relational operators help in decision making in C++?

Relational operators are used in conditions to decide which code to run. For example, in an if statement, they check if a condition is true or false to choose the path.

beginner

What is the difference between == and = in C++?

== is a relational operator that checks if two values are equal.
= is an assignment operator that sets a value to a variable.
Using = instead of == in a condition causes errors or unexpected behavior.

Which operator checks if two values are NOT equal in C++?

A !=

B ==

C <=

D >=

The operator != means 'not equal to' and returns true if values differ.

What does the expression (7 > 3) return in C++?

A false

B 1

C 0

D Error

7 is greater than 3, so (7 > 3) is true, which prints as 1.

Which relational operator means 'less than or equal to'?

A >=

B ==

C <=

D !=

The operator <= means 'less than or equal to'.

What is the result of (5 == 5) in C++?

A false

B 5

C Error

D true

5 equals 5, so (5 == 5) is true.

Which operator is used to assign a value to a variable?

A =

B <

C !=

D ==

The = operator assigns a value to a variable, not to compare.

Explain what relational operators do in C++ and give examples.

Think about how you check if one number is bigger or smaller than another.

Describe how relational operators are used in decision making with if statements.

Imagine deciding what to do based on comparing two things.

Practice

1.

Which of the following relational operators checks if two values are not equal in C++?

easy

A. >=

B. !=

C. <=

D. ==

Solution

1. Step 1: Understand the meaning of each operator

   The operator == checks equality, <= and >= check less or equal and greater or equal respectively.

2. Step 2: Identify the operator for 'not equal'

   The operator != means 'not equal' in C++.

3. Final Answer:

   != -> Option B

4. Quick Check:

   Not equal operator = != [OK]

Hint: Remember: != means not equal in C++ [OK]

Common Mistakes:

• Confusing == with !=
• Thinking <= means not equal
• Mixing up >=
• Using = instead of ==

2.

Which of the following is the correct syntax to compare if a is greater than b in C++?

int a = 5, b = 3;
if (___) {
    // code
}

easy

A. a > b

B. a => b

C. a >< b

D. a >= b

Solution

1. Step 1: Recall the correct operator for 'greater than'

   The operator for 'greater than' is >. The operator >= means 'greater than or equal to'.

2. Step 2: Check syntax correctness

   a > b is the correct syntax to check if a is strictly greater than b. Other options are invalid syntax.

3. Final Answer:

   a > b -> Option A

4. Quick Check:

   Greater than operator = > [OK]

Hint: Use > for greater than, >= for greater or equal [OK]

Common Mistakes:

• Using => instead of >=
• Using >< which is invalid
• Confusing >= with >
• Missing spaces causing syntax errors

3.

What will be the output of the following C++ code?

int x = 7, y = 10;
if (x <= y) {
    std::cout << "Yes";
} else {
    std::cout << "No";
}

medium

A. No

B. 10

C. 7

D. Yes

Solution

1. Step 1: Evaluate the relational expression

   Check if x <= y means 7 is less than or equal to 10, which is true.

2. Step 2: Determine which branch executes

   Since the condition is true, the if block runs and prints "Yes".

3. Final Answer:

   Yes -> Option D

4. Quick Check:

   7 <= 10 is true, so output is Yes [OK]

Hint: Check condition truth to decide output [OK]

Common Mistakes:

• Confusing <= with <
• Assuming else block runs
• Printing variable values instead of strings
• Ignoring the condition result

4.

Find the error in the following C++ code snippet:

int a = 4, b = 9;
if (a = b) {
    std::cout << "Equal";
} else {
    std::cout << "Not Equal";
}

medium

A. Incorrect variable declaration

B. Missing semicolon after if statement

C. Using assignment operator instead of equality operator in if condition

D. Using std::cout incorrectly

Solution

1. Step 1: Identify the operator in the if condition

   The condition uses a = b, which assigns value of b to a instead of comparing.

2. Step 2: Correct the operator for comparison

   To compare, the operator should be ==, so the condition should be a == b.

3. Final Answer:

   Using assignment operator instead of equality operator in if condition -> Option C

4. Quick Check:

   Use == for comparison, not = [OK]

Hint: Use == to compare, = to assign [OK]

Common Mistakes:

• Using = instead of ==
• Forgetting to compare variables
• Assuming assignment returns boolean false
• Ignoring compiler warnings

5.

Given the code below, what will be the output?

int a = 5, b = 5, c = 10;
if (a == b && c > b) {
    std::cout << "Match";
} else if (a != b || c < b) {
    std::cout << "Mismatch";
} else {
    std::cout << "Unknown";
}

hard

A. Match

B. Unknown

C. Mismatch

D. Compilation error

Solution

1. Step 1: Evaluate the first if condition

   Check a == b (5 == 5) is true, and c > b (10 > 5) is true, so the whole condition is true.

2. Step 2: Determine which block executes

   Since the first condition is true, "Match" is printed and the rest is skipped.

3. Final Answer:

   Match -> Option A

4. Quick Check:

   Both conditions true, so output is Match [OK]

Hint: Check && needs both true, || needs one true [OK]

Common Mistakes:

• Confusing && and || operators
• Ignoring short-circuit evaluation
• Assuming else if runs after true if
• Misreading relational comparisons