Blockchain - Smart Contracts

Smart Contract Example: Simple Token

Introduction

This smart contract demonstrates a basic token on the Ethereum blockchain. It implements essential features such as token transfers, allowance, and approval mechanisms.

Smart Contract Code

Solidity Code

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

    contract SimpleToken {
        string public name = "SimpleToken";
        string public symbol = "STK";
        uint8 public decimals = 18;
        uint256 public totalSupply;
        mapping(address => uint256) public balanceOf;
        mapping(address => mapping(address => uint256)) public allowance;

        // Event declarations
        event Transfer(address indexed from, address indexed to, uint256 value);
        event Approval(address indexed owner, address indexed spender, uint256 value);

        constructor(uint256 _initialSupply) {
            totalSupply = _initialSupply * 10 ** uint256(decimals);
            balanceOf[msg.sender] = totalSupply;
        }

        // Transfer tokens from sender to recipient
        function transfer(address _to, uint256 _value) public returns (bool success) {
            require(_to != address(0), "Invalid address");
            require(balanceOf[msg.sender] >= _value, "Insufficient balance");

            balanceOf[msg.sender] -= _value;
            balanceOf[_to] += _value;
            emit Transfer(msg.sender, _to, _value);
            return true;
        }

        // Approve a spender to withdraw tokens from the sender's account
        function approve(address _spender, uint256 _value) public returns (bool success) {
            allowance[msg.sender][_spender] = _value;
            emit Approval(msg.sender, _spender, _value);
            return true;
        }

        // Transfer tokens from an approved spender
        function transferFrom(address _from, address _to, uint256 _value) public returns (bool success) {
            require(_from != address(0), "Invalid sender address");
            require(_to != address(0), "Invalid recipient address");
            require(balanceOf[_from] >= _value, "Insufficient balance");
            require(allowance[_from][msg.sender] >= _value, "Allowance exceeded");

            balanceOf[_from] -= _value;
            balanceOf[_to] += _value;
            allowance[_from][msg.sender] -= _value;
            emit Transfer(_from, _to, _value);
            return true;
        }
    }
    
    

Breakdown of the Smart Contract

State Variables

• name, symbol, decimals: Basic attributes of the token.
• totalSupply: Total number of tokens available.
• balanceOf: A mapping that holds the token balance for each address.
• allowance: A mapping to track how much a spender is allowed to withdraw from a user’s account.

Events

• Transfer: Triggered when tokens are transferred between addresses.
• Approval: Triggered when a user approves another address to spend tokens on their behalf.

Constructor

The constructor initializes the total supply and assigns it to the creator's address.

Functions

• transfer(): Allows a user to send tokens to another address.
• approve(): Lets a user approve another address to spend tokens on their behalf.
• transferFrom(): Allows an approved address to spend tokens from the sender’s account.

This smart contract is a basic example of how to implement token functionality on the Ethereum blockchain. It can be extended further for more complex use cases like staking, token burning, or governance.