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function withdraw(uint amount) external {
    require(balances[msg.sender] >= amount);
    // ⚠️ External call before state update
    (bool ok, ) = msg.sender.call{value: amount}("");
    require(ok);
    balances[msg.sender] -= amount;
}

// Solidity < 0.8.0 — no built-in overflow check
uint8 balance = 255;
balance += 1; // ⚠️ Wraps to 0

// ✅ Use SafeMath or Solidity >= 0.8.0
balance = balance + 1; // Reverts on overflow

// ⚠️ Missing access control
function setPrice(uint _price) external {
    price = _price;
}

// ✅ With proper modifier
function setPrice(uint _price) external onlyOwner {
    price = _price;
}

// ⚠️ Price derived from single pool — manipulable
uint price = reserveA / reserveB;

// ✅ Use time-weighted average price (TWAP)
uint price = oracle.consult(token, period);

// ⚠️ Vulnerable to sandwich attack
function swap(uint amountIn) external {
    uint amountOut = getAmountOut(amountIn);
    token.transfer(msg.sender, amountOut);
}

// ✅ Use minimum output amount
function swap(uint amountIn, uint minOut) external {
    uint amountOut = getAmountOut(amountIn);
    require(amountOut >= minOut, "Slippage");
    token.transfer(msg.sender, amountOut);
}

// ⚠️ Ignoring return value
token.transfer(to, amount);

// ✅ Check return value
bool success = token.transfer(to, amount);
require(success, "Transfer failed");

// ✅ Or use SafeERC20
SafeERC20.safeTransfer(token, to, amount);