snippet from my Solidity smart contract

MyContract.sol

function supplyErc20ToCompound(
  address _erc20Contract,
  address _cErc20Contract,
  uint256 _numTokensToSupply
) public returns (uint) {
  // Create a reference to the underlying asset contract, like DAI.
  Erc20 underlying = Erc20(_erc20Contract);

  // Create a reference to the corresponding cToken contract, like cDAI
  CErc20 cToken = CErc20(_cErc20Contract);

  // Approve transfer on the ERC20 contract
  underlying.approve(_cErc20Contract, _numTokensToSupply);

  // Mint cTokens and return the result
  uint mintResult = cToken.mint(_numTokensToSupply);
  return mintResult;
}