contract ERC20 { string public name; string public symbol; mapping(address => uint256) public balanceOf; address public owner; uint8 public decimals; uint256 public totalSupply; // owner -> spender -> allowance // this enables an owner to give allowance to multiple addresses mapping(address => mapping(address => uint256)) public allowance; constructor(string memory _name, string memory _symbol) { name = _name; symbol = _symbol; decimals = 18; owner = msg.sender; } function mint(address to, uint256 amount) public { require(msg.sender == owner, "only owner can create tokens"); totalSupply += amount; balanceOf[owner] += amount; } function transfer(address to, uint256 amount) public returns (bool) { require(balanceOf[msg.sender] >= amount, "you aint rich enough"); require(to != address(0), "cannot send to address(0)"); balanceOf[msg.sender] -= amount; balanceOf[to] += amount; return true; } function approve(address spender, uint256 amount) public returns (bool) { allowance[msg.sender][spender] = amount; return true; } // just added function transferFrom(address from, address to, uint256 amount) public returns (bool) { require(balanceOf[from] >= amount, "not enough money"); require(to != address(0), "cannot send to address(0)"); if (msg.sender != from) { require(allowance[from][msg.sender] >= amount, "not enough allowance"); allowance[from][msg.sender] -= amount; } balanceOf[from] -= amount; balanceOf[to] += amount; return true; } }
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