Ethereum Virtual Machine (EVM) in Blockchain / Solidity - Interactive Code Practice

Practice - 5 Tasks

1fill in blank

easy

Complete the code to declare a simple EVM bytecode sequence that stops execution.

Blockchain / Solidity

bytecode = [[1]]

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

A0x56

B0x60

C0xF3

D0x00

Attempts:

3 left

💡 Hint

Common Mistakes

Using PUSH1 (0x60) instead of STOP.

Using JUMP (0x56) which jumps to a location.

Using RETURN (0xF3) which returns data.

The opcode 0x00 is the STOP instruction in EVM, which halts execution.

2fill in blank

medium

Complete the code to push the value 0x05 onto the EVM stack.

Blockchain / Solidity

bytecode = [[1], 0x05]

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

A0x60

B0x01

C0x50

D0x56

Attempts:

3 left

💡 Hint

Common Mistakes

Using JUMP (0x56) instead of PUSH1.

Using POP (0x50) which removes from stack.

Using ADD (0x01) which adds top stack items.

The opcode 0x60 is PUSH1, which pushes the next 1 byte onto the stack.

3fill in blank

hard

Fix the error in the code to correctly add two numbers on the EVM stack.

Blockchain / Solidity

bytecode = [0x60, 0x03, 0x60, 0x04, [1]]

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

A0x50

B0x01

C0x02

D0x56

Attempts:

3 left

💡 Hint

Common Mistakes

Using JUMP (0x56) instead of ADD.

Using POP (0x50) which removes stack items.

Using MUL (0x02) which multiplies instead of adds.

The opcode 0x01 is ADD, which adds the top two stack values.

4fill in blank

hard

Fill both blanks to create bytecode that pushes 0x02 and 0x03, then multiplies them.

Blockchain / Solidity

bytecode = [[1], 0x02, [2], 0x03, 0x02]

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

A0x60

B0x01

D0x03

Attempts:

3 left

💡 Hint

Common Mistakes

Using ADD (0x01) or MUL (0x02) instead of PUSH1 for pushing values.

Mixing up opcodes for pushing and arithmetic.

Both 0x60 opcodes push 1 byte values (0x02 and 0x03) onto the stack before multiplication.

5fill in blank

hard

Fill all three blanks to push 0x04 and 0x05, add them, then stop execution.

Blockchain / Solidity

bytecode = [[1], 0x04, [2], 0x05, 0x01, [3]]

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

A0x60

B0x01

C0x00

D0x50

Attempts:

3 left

💡 Hint

Common Mistakes

Using POP (0x50) instead of STOP.

Forgetting to push both values.

Using wrong opcode for addition or stop.

Use PUSH1 (0x60) twice to push 0x04 and 0x05, then ADD (0x01) to add them, and STOP (0x00) to end execution.

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