Ethereum Virtual Machine (EVM) in Blockchain / Solidity - Mini Project: Build & Apply

Understanding Ethereum Virtual Machine (EVM) Basics

📖 Scenario: You are learning how the Ethereum Virtual Machine (EVM) executes smart contracts. To understand this, you will create a simple Solidity contract that stores and retrieves a number. This simulates how data is stored and accessed on the blockchain through the EVM.

🎯 Goal: Build a simple Solidity smart contract that stores a number and allows reading it back. This will help you understand how the EVM handles contract storage and function calls.

📋 What You'll Learn

Create a Solidity contract named SimpleStorage

Add a state variable storedNumber of type uint

Add a function storeNumber that takes a uint parameter and saves it to storedNumber

Add a function retrieveNumber that returns the current value of storedNumber

Print the retrieved number after storing it

💡 Why This Matters

🌍 Real World

Smart contracts on Ethereum use the EVM to store and manage data securely and transparently. Understanding how to store and retrieve data is fundamental to building decentralized applications.

💼 Career

Blockchain developers must know how to write Solidity contracts that interact with the EVM. This project builds foundational skills for creating and testing smart contracts.

1

Create the Solidity contract and state variable

Write a Solidity contract named SimpleStorage. Inside it, declare a state variable called storedNumber of type uint to hold a number.

Blockchain / Solidity

pragma solidity ^0.8.0;

contract SimpleStorage {
    // Declare storedNumber here
}

Hint

Use contract SimpleStorage { } to start the contract and uint storedNumber; to declare the variable.

2

Add a function to store a number

Inside the SimpleStorage contract, add a public function named storeNumber that takes a uint parameter called num and assigns it to storedNumber.

Blockchain / Solidity

pragma solidity ^0.8.0;

contract SimpleStorage {
    uint storedNumber;

    // Add storeNumber function here
}

Hint

Define function storeNumber(uint num) public { storedNumber = num; } inside the contract.

3

Add a function to retrieve the stored number

Add a public view function named retrieveNumber inside SimpleStorage that returns the current value of storedNumber as a uint.

Blockchain / Solidity

pragma solidity ^0.8.0;

contract SimpleStorage {
    uint storedNumber;

    function storeNumber(uint num) public {
        storedNumber = num;
    }

    // Add retrieveNumber function here
}

Hint

Use function retrieveNumber() public view returns (uint) { return storedNumber; } to read the stored number.

4

Test storing and retrieving a number

Write a script or test code that creates an instance of SimpleStorage, calls storeNumber(42), then calls retrieveNumber() and prints the returned value.

Blockchain / Solidity

pragma solidity ^0.8.0;

contract SimpleStorage {
    uint storedNumber;

    function storeNumber(uint num) public {
        storedNumber = num;
    }

    function retrieveNumber() public view returns (uint) {
        return storedNumber;
    }
}

// Call storeNumber(42) and print retrieveNumber() result
// Your code here

Hint

After deploying, call storeNumber(42) then retrieveNumber() to see 42 returned.

Practice

1. What is the main role of the Ethereum Virtual Machine (EVM) in the Ethereum network?

easy

A. It executes smart contract bytecode to run decentralized applications.

B. It stores user account balances and transaction history.

C. It mines new Ethereum blocks using proof of work.

D. It manages the Ethereum wallet user interface.

Solution

1. Step 1: Understand EVM's purpose

   The EVM is a virtual computer that runs smart contracts on Ethereum.

2. Step 2: Identify correct role

   It executes compiled bytecode from smart contracts, enabling decentralized apps to run safely and consistently.

3. Final Answer:

   It executes smart contract bytecode to run decentralized applications. -> Option A

4. Quick Check:

   EVM runs smart contracts = B [OK]

Hint: EVM runs code, not stores or mines [OK]

Common Mistakes:

• Confusing EVM with blockchain storage
• Thinking EVM mines blocks
• Mixing EVM with wallet software

2. Which of the following is the correct way to represent a simple EVM instruction to add two numbers?

easy

A. ADD 5 3

B. PUSH1 5 PUSH1 3 ADD

C. LOAD 5 3 ADD

D. SUM 5 3

Solution

1. Step 1: Recall EVM instruction format

   EVM uses stack operations like PUSH1 to push values, then ADD to add top stack items.

2. Step 2: Identify correct instruction sequence

   "PUSH1 5 PUSH1 3 ADD" pushes 5 and 3, then adds them on the stack.

3. Final Answer:

   PUSH1 5 PUSH1 3 ADD -> Option B

4. Quick Check:

   Push values then add = C [OK]

Hint: EVM uses PUSH and then operation instructions [OK]

Common Mistakes:

• Using invalid instructions like ADD 5 3 directly
• Confusing LOAD with PUSH
• Using non-EVM commands like SUM

3. Given this EVM bytecode snippet:

PUSH1 0x02
PUSH1 0x03
ADD

What is the result on the stack after execution?

medium

A. 0x05

B. 0x06

C. 0x23

D. 0x00

Solution

1. Step 1: Understand PUSH1 and ADD operations

   PUSH1 0x02 pushes 2, PUSH1 0x03 pushes 3, ADD adds top two stack values.

2. Step 2: Calculate addition result

   2 + 3 = 5, so 0x05 remains on the stack.

3. Final Answer:

   0x05 -> Option A

4. Quick Check:

   2 + 3 = 5 = 0x05 [OK]

Hint: Add pushed hex values on stack [OK]

Common Mistakes:

• Adding hex as strings instead of numbers
• Confusing 0x02 + 0x03 as 0x06
• Misreading PUSH1 as PUSH2

4. Identify the error in this EVM bytecode sequence:

PUSH1 0x01
ADD

medium

A. No error; code is correct.

B. PUSH1 opcode is invalid.

C. ADD cannot be used after PUSH1.

D. Missing second operand on stack for ADD instruction.

Solution

1. Step 1: Check stack before ADD

   PUSH1 0x01 pushes one value, but ADD needs two values on stack.

2. Step 2: Identify missing operand

   Since only one value is pushed, ADD causes stack underflow error.

3. Final Answer:

   Missing second operand on stack for ADD instruction. -> Option D

4. Quick Check:

   ADD needs two stack values [OK]

Hint: ADD requires two values on stack [OK]

Common Mistakes:

• Assuming ADD works with one operand
• Thinking PUSH1 is invalid
• Believing code is correct as is

5. You want to write an EVM bytecode sequence that calculates (4 + 5) * 3. Which sequence correctly achieves this?

hard

A. PUSH1 0x03 PUSH1 0x04 ADD PUSH1 0x05 MUL

B. PUSH1 0x04 PUSH1 0x05 MUL PUSH1 0x03 ADD

C. PUSH1 0x04 PUSH1 0x05 ADD PUSH1 0x03 MUL

D. PUSH1 0x04 PUSH1 0x03 MUL PUSH1 0x05 ADD

Solution

1. Step 1: Understand operation order

   (4 + 5) * 3 means add 4 and 5 first, then multiply by 3.

2. Step 2: Match EVM instructions to operations

   PUSH1 0x04 PUSH1 0x05 ADD pushes 4 and 5, adds them; then PUSH1 0x03 MUL multiplies result by 3.

3. Step 3: Check other options

   Options B, C, and D change operation order or operands, producing incorrect results (B: 23, C: 35, D: 17).

4. Final Answer:

   PUSH1 0x04 PUSH1 0x05 ADD PUSH1 0x03 MUL -> Option C

5. Quick Check:

   Add then multiply = A [OK]

Hint: Add first, then multiply in EVM code [OK]

Common Mistakes:

• Changing operation order incorrectly
• Confusing MUL and ADD positions
• Ignoring operator precedence