slide 21 · contracts

Solidity syntax & coding

pragma solidity

contract Counter {

uint256 public n;

function inc()

6080604052

34801561001

0f3560e01c

bytecode

Walk a line by line: pragma, , visibility, modifiers, events.

1Step through the contract line by line
2Read what each keyword does
3Compile it to bytecode

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Token.sol — click a concept to highlight it

 1// SPDX-License-Identifier: MIT
 2pragma solidity ^0.8.24;
 3
 4contract Token {
 5    string public name = "DemoToken";
 6    uint8 public constant decimals = 18;
 7    address public immutable owner;
 8
 9    mapping(address => uint256) private _balances;
10
11    event Transfer(address indexed from, address indexed to, uint256 value);
12
13    error InsufficientBalance(uint256 have, uint256 want);
14
15    modifier onlyOwner() {
16        require(msg.sender == owner, "not owner");
17        _;
18    }
19
20    constructor(uint256 supply) {
21        owner = msg.sender;
22        _balances[msg.sender] = supply;
23    }
24
25    function balanceOf(address a) external view returns (uint256) {
26        return _balances[a];
27    }
28
29    function transfer(address to, uint256 amount) external returns (bool) {
30        uint256 bal = _balances[msg.sender];
31        if (bal < amount) revert InsufficientBalance(bal, amount);
32        _balances[msg.sender] = bal - amount;
33        _balances[to] += amount;
34        emit Transfer(msg.sender, to, amount);
35        return true;
36    }
37
38    function mint(address to, uint256 amount) external onlyOwner {
39        _balances[to] += amount;
40    }
41}

1 / 10 · License & pragma

The SPDX comment declares the license (the compiler warns without it). The pragma pins a compiler version range — ^0.8.24 means 0.8.24 up to but excluding 0.9.0. From 0.8.0 onward, arithmetic reverts on overflow by default.

Concepts

Workflow to remember: write in Remix or Foundry → compile to bytecode + ABI → test → deploy to a testnet (Sepolia) → verify the source on Etherscan so users can read what they are trusting.