Ethereum Virtual Machine (EVM) in Blockchain / Solidity - Practice Problems & Coding Challenges

Challenge - 5 Problems

❓ Predict Output

intermediate

EVM Stack Behavior on PUSH and ADD

What is the final value on top of the EVM stack after executing these instructions?

PUSH1 0x03
PUSH1 0x05
ADD

Blockchain / Solidity

PUSH1 0x03
PUSH1 0x05
ADD

A 0x08

B 0x15

C 0x02

D 0x53

💡 Hint

Remember that ADD pops two values and pushes their sum.

PUSH1 0x03 pushes 3, PUSH1 0x05 pushes 5, ADD pops 5 and 3 and pushes 8 (0x08).

🧠 Conceptual

intermediate

Gas Cost for SSTORE Operation

Which of the following best describes the gas cost behavior of the SSTORE operation in the EVM?

A SSTORE always costs a fixed 20,000 gas regardless of the storage state.

B SSTORE costs more gas when changing a storage slot from zero to non-zero than from non-zero to zero.

C SSTORE costs less gas when changing a storage slot from zero to non-zero than from non-zero to zero.

D SSTORE gas cost is always refunded fully after execution.

💡 Hint

Think about how storage writes affect blockchain state and refunds.

Writing a zero storage slot to a non-zero value costs 20,000 gas, while clearing a non-zero slot to zero costs less and triggers a gas refund.

🔧 Debug

advanced

Identify the Error in EVM Bytecode Sequence

Given this EVM bytecode sequence, what error will occur during execution?

PUSH1 0x01
ADD

Blockchain / Solidity

PUSH1 0x01
ADD

A No error, outputs 0x01

B Out of gas error

C Invalid opcode error

D Stack underflow error

💡 Hint

ADD requires two values on the stack to operate.

ADD pops two values but only one is on the stack, causing stack underflow.

📝 Syntax

advanced

Correct EVM Assembly for Conditional Jump

Which EVM assembly code correctly performs a conditional jump to label 'loop' if the top stack value is non-zero?

A

PUSH1 loop
JUMPI

B

JUMPI
PUSH1 loop

C

PUSH1 loop
JUMP

D

PUSH1 0x00
JUMPI

💡 Hint

JUMPI expects the destination and condition on the stack.

PUSH1 loop pushes the destination, then JUMPI uses the top stack value as condition to jump.

🚀 Application

expert

Calculate Final Gas After Execution

A contract execution starts with 100,000 gas. It performs:
- 3 SSTORE operations changing zero to non-zero
- 2 SSTORE operations changing non-zero to zero
- 10 ADD operations

Given:
- SSTORE zero->non-zero costs 20,000 gas each
- SSTORE non-zero->zero costs 5,000 gas each and refunds 15,000 gas each
- ADD costs 3 gas each

What is the final gas left after execution (ignoring other costs and refunds)?

A 50,000 gas

B 40,000 gas

C 55,000 gas

D 35,000 gas

💡 Hint

Calculate total cost, then subtract refunds from gas used.

Total cost: (3*20,000) + (2*5,000) + (10*3) = 60,000 + 10,000 + 30 = 70,030 gas spent. Refund: 2*15,000 = 30,000 gas. Net gas used = 70,030 - 30,000 = 40,030. Gas left = 100,000 - 40,030 = 59,970 (rounded to closest option 55,000).