Token Sale Smart Contract

Question

I am new to Ethereium Block Chain and have been trying some code written in solidity as follows.

pragma solidity ^0.5.0;

import "./MyERC20Token.sol";
import "./ERC20Burnable.sol";


contract MyERC20TokenSale {
address payable admin;
MyERC20Token public tokenContract;
uint256 public tokenPrice;
uint256 public tokensSold;

event Sell(address _buyer, uint256 _amount);

constructor(MyERC20Token _tokenContract, uint256 _tokenPrice) public {
    admin = msg.sender;
    tokenContract = _tokenContract;
    tokenPrice = _tokenPrice;
}

function multiply(uint x, uint y) internal pure returns (uint z) {
    require(y == 0 || (z = x * y) / y == x);
}

function buyTokens(uint256 _numberOfTokens) public payable {
    require(msg.value == multiply(_numberOfTokens, tokenPrice));
    require(tokenContract.balanceOf(address(this)) >= _numberOfTokens);
    require(tokenContract.transfer(msg.sender, _numberOfTokens));

    tokensSold += _numberOfTokens;

    emit Sell(msg.sender, _numberOfTokens);
}

function endSale() public {
    require(msg.sender == admin);
    require(tokenContract.transfer(admin, tokenContract.balanceOf(address(this))));

    admin.transfer(address(this).balance);
}
 }

I wish to return all the raised tokens to the admin and burn the unused tokens. But when I am doing endSale(), I am getting Error : invalid opcode.

It will be a really helping if someone can go through this code.

Answer 1

require(msg.sender == admin);

You need to send the transaction from the same account that deployed the contract. admin was set at deployment time with admin = msg.sender; in the constructor.

require(tokenContract.transfer(admin, tokenContract.balanceOf(address(this))));

Transfers the token balance of the sale contract to the admin. Should be okay.

admin.transfer(address(this).balance);

Transfer the ether balance to admin. Should be okay.

Best guess is you are not meeting the first requirement.

Hope it helps.

Answer 2

The issue is resolved by changing pragma solidity ^0.5.0 to pragma solidity ^0.5.1. It is working now. Thanks for the help.