Gas optimization for L2 in Blockchain / Solidity - Interactive Code Practice

Practice - 5 Tasks

1fill in blank

easy

Complete the code to declare a fixed-size array to save gas on L2.

Blockchain / Solidity

uint256[[1]] public fixedArray;

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A0

B10

Cdynamic

Duint256

Attempts:

3 left

💡 Hint

Common Mistakes

Using dynamic arrays which cost more gas.

Setting size to zero which is invalid.

Using a fixed-size array like uint256[10] helps save gas on L2 by avoiding dynamic array overhead.

2fill in blank

medium

Complete the code to use calldata for function parameters to save gas on L2.

Blockchain / Solidity

function processData(string[1] data) external {}

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A memory

B storage

C calldata

D public

Attempts:

3 left

💡 Hint

Common Mistakes

Using memory which copies data and costs more gas.

Using storage which is not allowed for function parameters.

Using calldata for external function parameters saves gas because it avoids copying data into memory.

3fill in blank

hard

Fix the error in the code to optimize gas by packing variables.

Blockchain / Solidity

contract GasSaver {
    uint128 public a;
    uint[1] public b;
}

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A128

B256

C64

D32

Attempts:

3 left

💡 Hint

Common Mistakes

Using uint256 which wastes storage slots.

Using different sizes that prevent packing.

Using uint128 for both variables allows Solidity to pack them into one storage slot, saving gas.

4fill in blank

hard

Fill both blanks to optimize gas by using unchecked math and short-circuiting.

Blockchain / Solidity

function increment(uint256 x) public pure returns (uint256) {
    uint256 y = unchecked { x [1] 1 };
    return y [2] 0 ? y : 0;
}

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A+

B>

C<

D-

Attempts:

3 left

💡 Hint

Common Mistakes

Using subtraction which may cause underflow.

Using wrong comparison operators that break logic.

Using unchecked with + avoids overflow checks, saving gas. The comparison y > 0 short-circuits unnecessary operations.

5fill in blank

hard

Fill all three blanks to optimize gas by using short-circuit evaluation, minimal storage writes, and efficient loops.

Blockchain / Solidity

function sum(uint256[] memory data) public pure returns (uint256) {
    uint256 total = 0;
    for (uint256 i = 0; i [1] data.length; i++) {
        if (data[i] [2] 0) {
            total [3]= data[i];
        }
    }
    return total;
}

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

A<=

B>

C+

D-

E<

Attempts:

3 left

💡 Hint

Common Mistakes

Using <= in loop condition causing out-of-bounds.

Adding zero values wasting gas.

Using -= instead of += causing wrong results.

Using i < data.length avoids out-of-bounds errors. Checking data[i] > 0 skips zero values to save gas. Using += efficiently accumulates the sum.