Smart contracts for dummies

Source: Dev.to

Introduction

Learning blockchain concepts can be challenging, but understanding smart contracts doesn’t have to be. This guide introduces the basics of smart contracts and walks through a simple “bank vault” contract written in Solidity.

Key Concepts

• State machine – The blockchain functions like a state machine (similar to Redux or Context API) that tracks and updates state.
• View – A read‑only operation that lets you see the current state, such as a contract’s balance.
• State – Data stored on the blockchain (e.g., balances, records).
• Contract – A piece of code that governs how state can be read or modified, analogous to a set of rules.
• Public – Functions or variables marked public can be accessed by anyone on the network.
• Remix – An online IDE for writing, testing, and deploying Solidity contracts.
• Returns – Specifies the output type of a function, typically used in view functions.

Example: Vault Contract

Below is a minimal Solidity contract that acts as a simple vault where users can deposit and withdraw Ether.

// SPDX-License-Identifier: MIT
pragma solidity ^0.8.20;

contract Vault {
    uint public initialBalance;
    uint public balance;

    constructor(uint _balance) {
        initialBalance = _balance;
        balance = _balance;
    }

    function checkBalance() public view returns (uint) {
        return balance;
    }

    function deposit(uint amount) public {
        balance += amount;
    }

    function withdraw(uint amount) public {
        require(balance >= amount, "Not enough balance");
        balance -= amount;
    }
}

Contract Overview

• State variables

  • initialBalance – Stores the balance set at deployment.
  • balance – Tracks the current vault balance.

• Constructor
  Initializes both initialBalance and balance with the value passed during deployment.

• Functions

  • checkBalance() – A view function that returns the current balance.
  • deposit(uint amount) – Increases balance by the specified amount.
  • withdraw(uint amount) – Decreases balance after verifying sufficient funds using require.

Important Details

• Parameter names prefixed with an underscore (e.g., _balance) avoid naming conflicts with state variables.
• The require statement acts like an if check; if the condition fails, the transaction reverts with the provided error message.
• All functions are marked public, making them callable by any external account.

Conclusion

The Vault contract demonstrates core Solidity concepts: state variables, constructors, view functions, state‑changing functions, and basic error handling. By experimenting with this example in Remix, you can gain a solid foundation for building more complex smart contracts.