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.