Short-circuiting in conditions in Blockchain / Solidity - Practice Problems & Coding Challenges

Challenge - 5 Problems

❓ Predict Output

intermediate

Output of short-circuit AND in Solidity

What is the output of this Solidity code snippet when executed?

Blockchain / Solidity

pragma solidity ^0.8.0;
contract Test {
    function check() public pure returns (string memory) {
        bool a = false;
        bool b = true;
        if (a && b) {
            return "Both true";
        } else {
            return "Short-circuited";
        }
    }
}

A "Short-circuited"

B "Both true"

C Compilation error

D Runtime error

💡 Hint

Remember that in AND conditions, if the first value is false, the second is not checked.

Since 'a' is false, the AND condition short-circuits and the else branch runs, returning "Short-circuited".

❓ Predict Output

intermediate

Output of short-circuit OR in Solidity

What will this Solidity function return when called?

Blockchain / Solidity

pragma solidity ^0.8.0;
contract Test {
    function check() public pure returns (string memory) {
        bool a = true;
        bool b = false;
        if (a || b) {
            return "Short-circuited OR";
        } else {
            return "Both false";
        }
    }
}

A "Short-circuited OR"

B Compilation error

C "Both false"

D Runtime error

💡 Hint

In OR conditions, if the first value is true, the second is not checked.

Since 'a' is true, the OR condition short-circuits and the if branch runs, returning "Short-circuited OR".

🔧 Debug

advanced

Identify the error caused by short-circuiting in Solidity

What error will this Solidity code produce when the function is called?

Blockchain / Solidity

pragma solidity ^0.8.0;
contract Test {
    uint x = 0;
    function check() public returns (uint) {
        if (x != 0 && (10 / x) > 1) {
            return 1;
        } else {
            return 0;
        }
    }
}

A Returns 1 always

B No error, returns 0

C Compilation error due to division

D Division by zero runtime error

💡 Hint

Think about how short-circuiting prevents division by zero.

Because 'x != 0' is false, the right side '(10 / x) > 1' is not evaluated, so no division by zero occurs and the function returns 0.

🧠 Conceptual

advanced

Understanding short-circuit evaluation in smart contracts

Why is short-circuit evaluation important in smart contract conditions?

A It disables all conditional checks

B It always causes runtime errors to be ignored

C It makes contracts run slower but safer

D It reduces gas costs by avoiding unnecessary computations

💡 Hint

Think about how blockchain charges for computation.

Short-circuit evaluation stops checking conditions early, saving computation steps and thus reducing gas costs.

❓ Predict Output

expert

Output of complex short-circuit condition in Solidity

What is the output of this Solidity function when called?

Blockchain / Solidity

pragma solidity ^0.8.0;
contract Test {
    uint public count = 0;
    function check() public returns (string memory) {
        if ((increment() > 0) || (increment() > 1)) {
            return "True";
        } else {
            return "False";
        }
    }
    function increment() internal returns (uint) {
        count += 1;
        return count;
    }
}

A "False" with count = 2

B "True" with count = 2

C "True" with count = 1

D "False" with count = 1

💡 Hint

Remember OR short-circuits after the first true condition.

The first call to increment() returns 1, which is > 0, so the OR condition short-circuits and the second increment() is not called. count is 1 and function returns "True".