Solidity - lesson 2 | HackIndia Skills

Solidity - lesson 2 | HackIndia Skills | HackIndia

Example

Readable contract state

This example stores student project submissions. It uses simple types, a struct for grouped data, a mapping for lookup, and an array for public listing.

Use this pattern when your hackathon contract needs records, owners, votes, tasks, certificates, or payments.

// SPDX-License-Identifier: MIT
pragma solidity ^0.8.0;

contract ProjectRegistry {
    uint256 public constant MAX_TITLE_LENGTH = 80;
    address public immutable admin;

    struct Project {
        address builder;
        string title;
        string repoUrl;
        bool submitted;
    }

    mapping(address => Project) public projectsByBuilder;
    address[] public builders;

    constructor() {
        admin = msg.sender;
    }

    function submitProject(string calldata title, string calldata repoUrl) external {
        require(bytes(title).length > 0, "Title required");
        require(bytes(title).length <= MAX_TITLE_LENGTH, "Title too long");
        require(!projectsByBuilder[msg.sender].submitted, "Already submitted");

        projectsByBuilder[msg.sender] = Project({
            builder: msg.sender,
            title: title,
            repoUrl: repoUrl,
            submitted: true
        });

        builders.push(msg.sender);
    }
}

Use types and data locations

One rule

Types you will use

Readable contract state

Pick the right type

Storage, memory, calldata

Use calldata first

Avoid old tutorial habits

Do this now

Quick check