Flashloan

flashloan.sol

contract YourContract {
  address aaveContractAddress;

  function initiateFlashLoan(address erc20token, uint256 amount) {
    Aave(aaveContractAddress).flashLoan(address(this), erc20token, amount);
  }

  function executeOperation(address erc20token, uint256 amount, uint256 fee) {
    // you're now approved for the "amount". do whatever you want with it

    // but don't forget to return it at the end
    ERC20(erc20token).transfer(aaveContractAddress, amount + fee);
  }
}


contract Aave {
  function flashLoan(address receiver, address erc20token, uint256 amount) {
    ERC20(erc20token).transfer(receiver, amount);
    uint256 fee = amount * 9 / 10000;

    YourContract(receiver).executeOperation(erc20token, amount, fee);

    // Get the funds back. If receiver contract did not "approve" the amount,
    // next line will fail and transaction will revert
    ERC20(erc20token).transferFrom(receiver, address(this), amount + fee);
  }
}