1// SPDX-License-Identifier: MIT
2pragma solidity ^0.8.0;
3 
4contract SimpleStorage {
5    uint256 public storedData;
6    
7    function set(uint256 x) public {
8        storedData = x;
9    }
10}

// SPDX-License-Identifier: MIT

Specifies the license. MIT is common for open-source. Required by Solidity compiler.

🔍 Key Solidity Concepts

State Variables

Variables stored permanently on blockchain. Cost gas to write, free to read.

uint256 myNumber; // Stored forever

Functions

Code that can be called externally or internally. Can modify state or just read.

function myFunction() public {}

Visibility Modifiers

Control who can access functions and variables.

public: Anyone can call (external or internal)

private: Only this contract

internal: This contract + inherited contracts

external: Only from outside the contract

🎯 What Does This Contract Do?

📥

Store a Number

Call set(42) to store 42 on blockchain

📤

Read the Number

Call storedData() to read current value

⛽

Gas Costs

Writing costs ~25,000 gas. Reading is FREE (doesn't modify state)

🌍

Public Data

Anyone can read or write. No access control (for simplicity)

💡 Common Data Types

Type	Description	Example
uint256	Unsigned integer (0 to 2^256-1)	uint256 age = 25;
int256	Signed integer (negative allowed)	int256 temp = -10;
address	Ethereum address (20 bytes)	address owner = 0x...
bool	Boolean (true/false)	bool isActive = true;
string	Text (UTF-8 encoded)	string name = "Alice";
bytes32	Fixed-size byte array	bytes32 hash = 0x...

✏️ Try It Yourself: Remix IDE

Step 1: Open Remix

Go to remix.ethereum.org in your browser

Step 2: Create File

File Explorer → contracts folder → New File → Name it SimpleStorage.sol

Step 3: Paste Code

Copy the SimpleStorage contract code and paste it into your file

Step 4: Save

Ctrl+S (Windows) or Cmd+S (Mac) to save. Remix auto-compiles!

🎓 Pro Tips

💡

Start Simple

Don't try to build complex contracts immediately. Master basics first!

📝

Comment Your Code

Use // for single-line or /* */ for multi-line comments. Explain WHY, not just what.

🔍

Read Other Contracts

Check verified contracts on Etherscan. Learn from production code!

🛡️

Test Everything

Always test on testnet before mainnet. Bugs cost real money on mainnet!