Enums in Blockchain / Solidity - Interactive Code Practice

Practice - 5 Tasks

1fill in blank

easy

Complete the code to declare an enum named Color with values Red, Green, and Blue.

Blockchain / Solidity

[1] Color {
    Red,
    Green,
    Blue
}

Drag options to blanks, or click blank then click option'

Aclass

Bcontract

Cstruct

Denum

Attempts:

3 left

💡 Hint

Common Mistakes

Using 'class' instead of 'enum' to declare an enum.

Using 'struct' which is for data structures, not enums.

In blockchain languages like Solidity, enum is used to declare an enumeration type.

2fill in blank

medium

Complete the code to assign the enum value Green to the variable favoriteColor.

Blockchain / Solidity

Color favoriteColor = Color.[1];

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ABlue

BGreen

CRed

DYellow

Attempts:

3 left

💡 Hint

Common Mistakes

Using a color not declared in the enum like 'Yellow'.

Forgetting to prefix with the enum type name.

To assign an enum value, use the enum type name followed by a dot and the value name.

3fill in blank

hard

Fix the error in the code to correctly compare if the variable currentStatus equals Status.Active.

Blockchain / Solidity

if (currentStatus [1] Status.Active) {
    // do something
}

Drag options to blanks, or click blank then click option'

A==

B=

C!=

D=>

Attempts:

3 left

💡 Hint

Common Mistakes

Using single equals = which assigns instead of compares.

Using arrow => which is not a comparison operator.

Use == to compare enum values for equality.

4fill in blank

hard

Fill both blanks to create a function that returns true if the input status is Pending.

Blockchain / Solidity

function isPending(Status status) public pure returns (bool) {
    return status [1] Status.[2];
}

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A==

B!=

CPending

DActive

Attempts:

3 left

💡 Hint

Common Mistakes

Using '!=' instead of '==' which would check for inequality.

Using the wrong enum value like 'Active' instead of 'Pending'.

The function compares the input status with Status.Pending using the equality operator ==.

5fill in blank

hard

Fill all three blanks to create a mapping from address to Status and a function to set the status.

Blockchain / Solidity

mapping(address => Status) public [1];

function setStatus(address user, Status newStatus) public {
    [2][user] = [3];
}

Drag options to blanks, or click blank then click option'

AuserStatus

BnewStatus

Cstatus

Duser

Attempts:

3 left

💡 Hint

Common Mistakes

Using different names for the mapping in declaration and assignment.

Assigning the wrong variable instead of newStatus.

The mapping is named userStatus. The function sets userStatus[user] to newStatus.

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