Enums in Blockchain / Solidity - Practice Problems & Coding Challenges

Challenge - 5 Problems

❓ Predict Output

intermediate

What is the output of this Solidity enum code?

Consider this Solidity contract snippet using an enum. What will be the output when getStatus() is called?

Blockchain / Solidity

pragma solidity ^0.8.0;

contract Order {
    enum Status { Pending, Shipped, Delivered, Cancelled }
    Status public status;

    constructor() {
        status = Status.Shipped;
    }

    function getStatus() public view returns (string memory) {
        if (status == Status.Pending) return "Pending";
        else if (status == Status.Shipped) return "Shipped";
        else if (status == Status.Delivered) return "Delivered";
        else return "Cancelled";
    }
}

A "Shipped"

B "Pending"

C "Delivered"

D "Cancelled"

💡 Hint

Look at the constructor and see which enum value is assigned to status.

The constructor sets status to Status.Shipped. The getStatus() function returns the string "Shipped" when the status matches Status.Shipped.

🧠 Conceptual

intermediate

What integer value does the first enum member have in Solidity?

In Solidity, enums start with the first member assigned which integer value?

A Undefined until assigned

B 1

C -1

D 0

💡 Hint

Think about how counting usually starts in programming.

In Solidity, enum members start counting from 0 by default. The first member has the value 0, the second 1, and so on.

🔧 Debug

advanced

Which option causes a runtime error in this Solidity enum usage?

Given this enum and function, which option will cause a runtime error?

enum Color { Red, Green, Blue }

function setColor(uint c) public pure returns (Color) {
    return Color(c);
}

A Calling setColor(1) returns Color.Green

B Calling setColor(0) returns Color.Red

C Calling setColor(3) causes an error

D Calling setColor(2) returns Color.Blue

💡 Hint

Check the valid range of enum values and what happens if you pass a number outside that range.

Enum values in Solidity correspond to integers starting at 0. The enum Color has 3 members (0 to 2). Passing 3 is out of range and causes a runtime error.

📝 Syntax

advanced

Which option correctly declares and uses an enum in Solidity?

Choose the correct Solidity code snippet that declares an enum and assigns a value to a state variable.

A

enum State { Active, Inactive }
State public state = State.Active;

B

enum State { Active, Inactive }
State public state = Active;

C

enum State { Active, Inactive }
State state = State[0];

D

enum State { Active, Inactive }
State state = 1;

💡 Hint

Remember how to refer to enum members with their enum type.

Option A correctly declares the enum and assigns the member using State.Active. Option A misses the enum type prefix. Option A uses invalid syntax with brackets. Option A assigns an integer directly without casting to the enum type, which is invalid in Solidity.

🚀 Application

expert

How many items are in the enum after this Solidity code runs?

Given this enum and contract, how many enum members exist?

pragma solidity ^0.8.0;

contract TrafficLight {
    enum Light { Red, Yellow, Green }

    function countLights() public pure returns (uint) {
        return uint(type(Light).max) + 1;
    }
}

A 2

B 3

C 4

D Compilation error

💡 Hint

Look at how type(Light).max relates to enum members.

The enum Light has three members: Red (0), Yellow (1), Green (2). The maximum value is 2, so adding 1 gives the total count 3.

Practice

1. What is the main purpose of using enum in blockchain programming?

easy

A. To execute smart contracts faster

B. To create random numbers for cryptography

C. To store large amounts of data efficiently

D. To group related named values together for clarity and safety

Solution

1. Step 1: Understand enum purpose

   Enums group related named values, making code easier to read and safer.

2. Step 2: Compare options

   Only To group related named values together for clarity and safety correctly describes enums' main purpose in blockchain code.

3. Final Answer:

   To group related named values together for clarity and safety -> Option D

4. Quick Check:

   Enums group named values = A [OK]

Hint: Enums group fixed options with names, not data or speed [OK]

Common Mistakes:

• Confusing enums with random number generators
• Thinking enums store large data
• Believing enums speed up contract execution

2. Which of the following is the correct syntax to declare an enum named Status with values Pending, Active, and Closed in Solidity?

easy

A. enum Status: Pending, Active, Closed

B. enum Status = (Pending, Active, Closed);

C. enum Status { Pending, Active, Closed }

D. enum Status { 'Pending', 'Active', 'Closed' }

Solution

1. Step 1: Recall Solidity enum syntax

   In Solidity, enums are declared with enum Name { Value1, Value2, ... } without equals or colons.

2. Step 2: Check each option

   enum Status { Pending, Active, Closed } matches correct syntax; others use invalid symbols or quotes.

3. Final Answer:

   enum Status { Pending, Active, Closed } -> Option C

4. Quick Check:

   Solidity enum syntax uses braces and commas = C [OK]

Hint: Enums use braces and commas, no equals or quotes [OK]

Common Mistakes:

• Using equals sign instead of braces
• Adding quotes around enum values
• Using colons instead of braces

3. Given the Solidity enum declaration:

enum Role { User, Admin, Guest }

and the code:

Role userRole = Role.Admin;
if (userRole == Role.Guest) {
    return "Guest Access";
} else {
    return "Not Guest";
}

What will be the output?

medium

A. "Not Guest"

B. "Guest Access"

C. Compilation error

D. Runtime error

Solution

1. Step 1: Understand enum values and assignment

   Role.Admin is assigned to userRole, which is not equal to Role.Guest.

2. Step 2: Evaluate the if condition

   The condition userRole == Role.Guest is false, so the else branch runs returning "Not Guest".

3. Final Answer:

   "Not Guest" -> Option A

4. Quick Check:

   Role.Admin != Role.Guest, so output = "Not Guest" [OK]

Hint: Compare enum values directly; Admin ≠ Guest means else runs [OK]

Common Mistakes:

• Assuming Admin equals Guest
• Expecting compilation or runtime errors
• Confusing enum names with strings

4. Identify the error in this Solidity enum usage:

enum State { Created, Locked, Inactive }
State public state;
function setState(uint _state) public {
    state = _state;
}

medium

A. Enum declaration syntax is wrong

B. Cannot assign uint directly to enum variable

C. Function setState should be private

D. Missing return type in function

Solution

1. Step 1: Analyze enum assignment

   Enums require assignment from enum values, not raw uint integers.

2. Step 2: Check function assignment

   Assigning _state (uint) directly to state (enum) causes a type mismatch error.

3. Final Answer:

   Cannot assign uint directly to enum variable -> Option B

4. Quick Check:

   Enum variables need enum values, not uints [OK]

Hint: Assign enum values, not integers, to enum variables [OK]

Common Mistakes:

• Assigning integers directly to enums
• Thinking enum syntax is wrong
• Confusing function visibility with errors

5. You want to represent user roles in a blockchain contract using enums. You need to check if a user has either Admin or Moderator role to allow special access. Given:

enum Role { User, Admin, Moderator, Guest }

Which of the following Solidity code snippets correctly checks for this condition?

hard

A. if (userRole == Role.Admin || userRole == Role.Moderator) { /* allow access */ }

B. if (userRole == Role.Admin && userRole == Role.Moderator) { /* allow access */ }

C. if (userRole in [Role.Admin, Role.Moderator]) { /* allow access */ }

D. if (userRole.equals(Role.Admin) || userRole.equals(Role.Moderator)) { /* allow access */ }

Solution

1. Step 1: Understand logical conditions for enums

   To allow access if userRole is Admin OR Moderator, use logical OR (||) between equality checks.

2. Step 2: Evaluate each option

   if (userRole == Role.Admin || userRole == Role.Moderator) { /* allow access */ } uses correct OR condition; B uses AND which is impossible; C uses invalid syntax; A uses non-existent method equals.

3. Final Answer:

   if (userRole == Role.Admin || userRole == Role.Moderator) { /* allow access */ } -> Option A

4. Quick Check:

   Use || for OR between enum comparisons [OK]

Hint: Use || to check multiple enum values, not && or invalid syntax [OK]

Common Mistakes:

• Using && instead of || for OR condition
• Trying to use 'in' keyword for enums
• Calling non-existent methods on enums