🔹 Final Smart Contract Optimization: A Step-by-Step Guide

Simple smart contract that calculates the sum of an array, and then shows how to optimize it for gas efficiency in three major steps. This is a practical example of how real-world Ethereum developers reduce gas costs.

Let’s break it down:

🧩 Original Smart Contract (Before Optimization)

pragma solidity ^0.8.0;

contract SumContract {
    uint256[] public arr = [1, 2, 3, 4, 5];
    uint256 public sum;

    function calculateSum() public {
        for (uint256 i = 0; i < arr.length; i++) {
            sum += arr[i];  // ❌ Problem: Modifying state in a loop
        }
    }
}

🔴 Issues with this code:

• It modifies a state variable (sum) inside a loop → very expensive in gas
• It reads directly from storage (arr) → slow and costly
• It uses checked arithmetic (default in Solidity 0.8+) → adds extra gas unless needed

✅ Step 1: Avoid State Variable Updates in Loops

❌ Problem:

sum += arr[i];  // Writes to storage every iteration!

• sum is a state variable → stored on blockchain
• Every update costs ~20,000 gas the first time, ~5,000 later
• Doing this in a loop multiplies the cost

✅ Solution:

Use a local variable in memory to accumulate the sum, then assign it to the state variable once at the end.