Relational operators in C++ - Practice Problems & Coding Challenges

Challenge - 5 Problems

❓ Predict Output

intermediate

Output of chained relational operators

What is the output of this C++ code snippet?

C++

#include <iostream>
int main() {
    int a = 5, b = 10, c = 15;
    std::cout << (a < b < c) << std::endl;
    return 0;
}

A Compilation error

B Undefined behavior

C 0

D 1

💡 Hint

Remember how chained comparisons are evaluated in C++.

In C++, the expression a < b < c is parsed left-to-right as (a < b) < c due to left associativity of relational operators.

a < b is true (value 1 when contextually converted to int).

Then 1 < c (1 < 15) is true (1).

Relational operators return bool; std::cout prints 1 for true.

❓ Predict Output

intermediate

Result of relational operator with mixed types

What is the output of this C++ code?

C++

#include <iostream>
int main() {
    int x = 7;
    double y = 7.0;
    std::cout << (x == y) << std::endl;
    return 0;
}

A 1

B Compilation error

C 0

D Runtime error

💡 Hint

Think about how C++ compares int and double.

The integer x is converted to double for comparison. Since 7 and 7.0 are equal, the expression x == y is true, so output is 1.

❓ Predict Output

advanced

Output of relational operators with pointers

What is the output of this C++ code snippet?

C++

#include <iostream>
int main() {
    int arr[3] = {1, 2, 3};
    int* p1 = &arr[0];
    int* p2 = &arr[2];
    std::cout << (p1 < p2) << std::endl;
    std::cout << (p2 < p1) << std::endl;
    return 0;
}

A Undefined behavior

B 1\n0

C Compilation error

D 0\n1

💡 Hint

Pointers to elements in the same array can be compared.

Pointer p1 points to arr[0], p2 points to arr[2]. Since p1 is before p2 in memory, p1 < p2 is true (1), and p2 < p1 is false (0).

❓ Predict Output

advanced

Relational operator with user-defined type and operator overloading

Given the following code, what is the output?

C++

#include <iostream>
class Box {
public:
    int volume;
    Box(int v) : volume(v) {}
    bool operator<(const Box& b) const {
        return volume < b.volume;
    }
};
int main() {
    Box b1(10), b2(20);
    std::cout << (b1 < b2) << std::endl;
    std::cout << (b2 < b1) << std::endl;
    return 0;
}

A 1\n0

B 0\n1

C Compilation error

D Runtime error

💡 Hint

Check how operator< is defined for Box.

The operator< compares volumes. Since 10 < 20 is true (1), and 20 < 10 is false (0), the output is 1 then 0.

🧠 Conceptual

expert

Behavior of relational operators with floating-point NaN values

In C++, what is the result of comparing a floating-point NaN (Not a Number) value with any number using relational operators like <, >, <=, >=?

A Comparisons cause a runtime error

B All comparisons return true except equality

C They all return false

D NaN is considered less than any number

💡 Hint

Think about how NaN behaves in floating-point comparisons.

According to IEEE floating-point rules, any comparison involving NaN returns false, except inequality (!=) which returns true. But relational operators (<, >, <=, >=) always return false when NaN is involved.

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