Blockchain Basics

This page covers the fundamental concepts of the QFC blockchain.

What is QFC?

QFC (Quantum Future Chain) is a high-performance, EVM-compatible blockchain that uses Proof of Contribution (PoC) consensus.

Key Components

Blocks

Blocks are containers that hold transactions and link together to form the blockchain.

interface Block {
  number: bigint;           // Block height
  hash: string;             // Block hash
  parentHash: string;       // Previous block hash
  timestamp: bigint;        // Unix timestamp
  producer: string;         // Validator who produced this block
  gasLimit: bigint;         // Maximum gas for this block
  gasUsed: bigint;          // Actual gas used
  transactionCount: number; // Number of transactions
}

Block Time: 3 seconds (average)

Transactions

Transactions are signed messages that transfer value or interact with smart contracts.

interface Transaction {
  hash: string;             // Transaction hash
  from: string;             // Sender address
  to: string | null;        // Recipient (null for contract creation)
  value: bigint;            // Amount transferred (in wei)
  gasLimit: bigint;         // Maximum gas
  gasPrice: bigint;         // Gas price (in wei)
  nonce: number;            // Transaction sequence number
  data: string;             // Input data (for contracts)
}

Accounts

QFC supports two types of accounts:

1. Externally Owned Accounts (EOA)

   • Controlled by private keys
   • Can send transactions
   • Has balance and nonce

2. Contract Accounts

   • Controlled by code
   • Can hold tokens and execute logic
   • Created by deploying a smart contract

State

The blockchain state is a mapping of addresses to account states:

State = {
  address1 => { balance, nonce, code, storage },
  address2 => { balance, nonce, code, storage },
  ...
}

State is stored in a Merkle Patricia Trie for efficient verification.

How Transactions Work

1. Creation: User creates and signs a transaction
2. Broadcasting: Transaction is sent to a node
3. Mempool: Transaction waits in the mempool
4. Inclusion: Validator includes transaction in a block
5. Execution: Transaction is executed, state is updated
6. Finality: Block is finalized (< 0.3 seconds)

// Example: Send a transaction
const tx = await wallet.sendTransaction({
  to: '0xRecipient...',
  value: parseQfc('10')
});

// Wait for confirmation
const receipt = await tx.wait();
console.log('Confirmed in block:', receipt.blockNumber);

Gas and Fees

Gas is a unit measuring computational effort:

• Gas Limit: Maximum gas you're willing to use
• Gas Price: Price per unit of gas (in wei)
• Transaction Fee: gasUsed × gasPrice

// Estimate gas for a transaction
const gasEstimate = await provider.estimateGas({
  to: '0x...',
  value: parseQfc('1')
});

// Get current gas price
const gasPrice = await provider.getGasPrice();

// Calculate fee
const fee = gasEstimate * gasPrice;
console.log('Estimated fee:', formatQfc(fee), 'QFC');

QFC fees are typically < $0.0001 per transaction.

Units

QFC uses 18 decimal places (same as Ethereum):

Unit	Wei	QFC
Wei	1	0.000000000000000001
Gwei	10^9	0.000000001
QFC	10^18	1

import { parseQfc, formatQfc, parseGwei } from '@qfc/sdk';

// Convert QFC to wei
const wei = parseQfc('1.5');     // 1500000000000000000n

// Convert wei to QFC
const qfc = formatQfc(wei);       // "1.5000"

// Parse gwei
const gwei = parseGwei('10');    // 10000000000n

Network Identifiers

Network	Chain ID	Currency
Testnet	9000	QFC
Mainnet	9001	QFC

Merkle Trees

QFC uses Merkle Patricia Tries for:

• State Trie: Current account states
• Transaction Trie: Transactions in a block
• Receipt Trie: Transaction receipts

This enables:

• Efficient state verification
• Light client support
• Proof of inclusion/exclusion

Consensus

See PoC Consensus for details on how blocks are produced and finalized.

Smart Contracts

QFC is EVM-compatible, supporting:

• Solidity smart contracts
• All EVM opcodes
• Standard token interfaces (ERC-20, ERC-721, etc.)

See Smart Contracts for more information.

Next Steps

• Accounts & Keys
• Transactions
• Gas & Fees