If-else statements in Blockchain / Solidity - Practice Problems & Coding Challenges

Challenge - 5 Problems

❓ Predict Output

intermediate

Output of a simple if-else in Solidity

What is the output of this Solidity function when value = 10?

Blockchain / Solidity

pragma solidity ^0.8.0;
contract Test {
    function checkValue(uint value) public pure returns (string memory) {
        if (value > 10) {
            return "Greater";
        } else if (value == 10) {
            return "Equal";
        } else {
            return "Less";
        }
    }
}

A "Less"

B "Greater"

C "Equal"

D Compilation error

💡 Hint

Check the condition that matches exactly 10.

The function returns "Equal" because the value is exactly 10, matching the else if condition.

❓ Predict Output

intermediate

If-else behavior with boolean in smart contract

What will the function return when flag = false?

Blockchain / Solidity

pragma solidity ^0.8.0;
contract FlagCheck {
    function checkFlag(bool flag) public pure returns (string memory) {
        if (flag) {
            return "True";
        } else {
            return "False";
        }
    }
}

A "False"

B Compilation error

C Runtime error

D "True"

💡 Hint

Think about what happens when the flag is false.

Since flag is false, the else branch runs and returns "False".

❓ Predict Output

advanced

Nested if-else output in Solidity

What does this function return when score = 75?

Blockchain / Solidity

pragma solidity ^0.8.0;
contract ScoreCheck {
    function grade(uint score) public pure returns (string memory) {
        if (score >= 90) {
            return "A";
        } else {
            if (score >= 80) {
                return "B";
            } else {
                if (score >= 70) {
                    return "C";
                } else {
                    return "F";
                }
            }
        }
    }
}

A "A"

B "F"

C "B"

D "C"

💡 Hint

Check each condition from top to bottom.

75 is less than 80 but greater or equal to 70, so it returns "C".

🧠 Conceptual

advanced

Error type from missing else in Solidity if-else

What error will this Solidity code produce when compiled?

Blockchain / Solidity

pragma solidity ^0.8.0;
contract Test {
    function check(uint x) public pure returns (string memory) {
        if (x > 5)
            return "High";
        else
            return "Low";
    }
}

A SyntaxError: 'else' without 'if'

B No error, returns "Low" for x <= 5

C TypeError: incompatible types

D Runtime error: unreachable code

💡 Hint

Look at the placement of else after a return statement.

The else is correctly placed after the if statement, so no syntax error occurs.

❓ Predict Output

expert

Output of complex if-else with multiple conditions

What is the output of this Solidity function when value = 15?

Blockchain / Solidity

pragma solidity ^0.8.0;
contract Complex {
    function test(uint value) public pure returns (string memory) {
        if (value < 10) {
            return "Less than 10";
        } else if (value < 20) {
            if (value % 2 == 0) {
                return "Even and less than 20";
            } else {
                return "Odd and less than 20";
            }
        } else {
            return "20 or more";
        }
    }
}

A "Odd and less than 20"

B "Even and less than 20"

C "20 or more"

D "Less than 10"

💡 Hint

Check if 15 is less than 20 and if it is even or odd.

15 is less than 20 and odd, so it returns "Odd and less than 20".