Function declaration and syntax in Blockchain / Solidity - Interactive Code Practice

Practice - 5 Tasks

1fill in blank

easy

Complete the code to declare a simple function named greet.

Blockchain / Solidity

function [1]() {
  return "Hello!";
}

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

Agreet

Bwelcome

CsayHello

Dhello

Attempts:

3 left

💡 Hint

Common Mistakes

Using a different function name than 'greet'.

Forgetting to write the function name after 'function'.

The function name must be greet as specified.

2fill in blank

medium

Complete the code to declare a function named add that takes two parameters a and b.

Blockchain / Solidity

function add([1], b) {
  return a + b;
}

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

Ax

Bnum

Ca

Dvalue

Attempts:

3 left

💡 Hint

Common Mistakes

Using a different parameter name than 'a'.

Mismatching parameter names with the function body.

The first parameter must be named a to match the function signature.

3fill in blank

hard

Fix the error in the function declaration by completing the missing keyword.

Blockchain / Solidity

[1] add(a, b) {
  return a + b;
}

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

Afunction

Bfunc

Cdef

Dmethod

Attempts:

3 left

💡 Hint

Common Mistakes

Using 'func' or 'def' instead of 'function'.

Omitting the function declaration keyword.

In blockchain smart contract languages like Solidity, the keyword function declares a function.

4fill in blank

hard

Fill both blanks to declare a public function named multiply that returns the product of two numbers.

Blockchain / Solidity

function [1](uint a, uint b) public returns (uint) {
  return a [2] b;
}

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

Amultiply

B+

C*

Dsubtract

Attempts:

3 left

💡 Hint

Common Mistakes

Using '+' instead of '*' for multiplication.

Using a wrong function name that does not match the operation.

The function name is 'multiply' and the operator for multiplication is '*'.

5fill in blank

hard

Fill all three blanks to declare a private function named subtract that takes two uint parameters and returns their difference.

Blockchain / Solidity

function [1](uint [2], uint [3]) private returns (uint) {
  return a - b;
}

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

Asubtract

Ba

Cb

Dadd

Attempts:

3 left

💡 Hint

Common Mistakes

Using incorrect parameter names that do not match the function body.

Using a wrong function name like 'add' instead of 'subtract'.

The function name is 'subtract', and the parameters are 'a' and 'b' to match the return statement.

Practice

1. What is the correct way to declare a function named transferFunds in a blockchain smart contract?

easy

A. transferFunds function() { }

B. function transferFunds() { }

C. func transferFunds() { }

D. def transferFunds() { }

Solution

1. Step 1: Identify the common function declaration keyword

   In many blockchain languages like Solidity, functions start with the keyword function.

2. Step 2: Check the syntax structure

   The correct syntax is function functionName() { }, so function transferFunds() { } is correct.

3. Final Answer:

   function transferFunds() { } -> Option B

4. Quick Check:

   Function declaration uses 'function' keyword [OK]

Hint: Look for 'function' keyword before name [OK]

Common Mistakes:

• Using 'def' instead of 'function'
• Placing 'function' after the name
• Using 'func' which is not standard here

2. Which of the following is the correct syntax to declare a function with one parameter named amount?

easy

A. function send(amount) { }

B. function send amount { }

C. function send(amount) => { }

D. function send[amount] { }

Solution

1. Step 1: Recognize parameter syntax in function declaration

   Parameters are placed inside parentheses separated by commas if multiple.

2. Step 2: Validate each option's syntax

   function send(amount) { } uses parentheses correctly: function send(amount) { }. Others misuse brackets, arrows, or omit parentheses.

3. Final Answer:

   function send(amount) { } -> Option A

4. Quick Check:

   Parameters go inside parentheses [OK]

Hint: Parameters always go inside parentheses () [OK]

Common Mistakes:

• Omitting parentheses around parameters
• Using square brackets instead of parentheses
• Using arrow syntax incorrectly

3. What will be the output of this function call in a blockchain smart contract?

function multiply(x, y) { return x * y; }
multiply(3, 4);

medium

A. 7

B. Error

C. 34

D. 12

Solution

1. Step 1: Understand the function logic

   The function multiplies two inputs x and y and returns the product.

2. Step 2: Calculate the result for inputs 3 and 4

   3 multiplied by 4 equals 12.

3. Final Answer:

   12 -> Option D

4. Quick Check:

   3 * 4 = 12 [OK]

Hint: Multiply inputs as given to get output [OK]

Common Mistakes:

• Adding instead of multiplying
• Concatenating numbers as strings
• Assuming syntax error without checking code

4. Identify the error in this function declaration:

function deposit(amount) {
  balance += amount
}

medium

A. Missing semicolon after statement

B. Function name is invalid

C. No return statement in function

D. Missing parentheses around parameter

Solution

1. Step 1: Check syntax inside the function body

   Statements inside functions usually require semicolons to end lines.

2. Step 2: Identify missing semicolon

   The line balance += amount lacks a semicolon at the end.

3. Final Answer:

   Missing semicolon after statement -> Option A

4. Quick Check:

   Statements need semicolons [OK]

Hint: Check for missing semicolons inside function body [OK]

Common Mistakes:

• Ignoring semicolon requirements
• Thinking return is mandatory
• Assuming function name is wrong

5. You want to create a function calculateFee that takes a transaction amount and returns 2% fee only if the amount is above 1000. Which is the correct function?

hard

A. function calculateFee(amount) { if amount > 1000 then return amount * 0.02 else return 0; }

B. function calculateFee(amount) { return amount * 0.02 if amount > 1000 else 0; }

C. function calculateFee(amount) { if (amount > 1000) { return amount * 0.02; } else { return 0; } }

D. function calculateFee(amount) { if (amount > 1000) return amount * 0.02; }

Solution

1. Step 1: Understand conditional return logic

   The function must check if amount is greater than 1000 and return 2% fee; otherwise, return 0.

2. Step 2: Validate syntax correctness

   function calculateFee(amount) { if (amount > 1000) { return amount * 0.02; } else { return 0; } } uses proper if-else syntax with braces and returns both cases correctly. Others have syntax errors or missing else return.

3. Final Answer:

   function calculateFee(amount) { if (amount > 1000) { return amount * 0.02; } else { return 0; } } -> Option C

4. Quick Check:

   Use if-else with braces for conditional returns [OK]

Hint: Use full if-else with braces for clear returns [OK]

Common Mistakes:

• Missing else return causes undefined output
• Incorrect if syntax without parentheses or braces
• Using Python-style if-else in blockchain code