coin.sol

pragma solidity ^0.5.3;

contract Owned{
    address public owner;

    constructor() public{
        owner = msg.sender;
    }

    modifier onlyOwner(){
        require(msg.sender == owner);
        _;
    }
}

contract Coin is Owned{
    mapping(address => uint) balances;
    uint decimals = 1**18;
    event Mint(address indexed destination, uint amount);

    /// @notice Mint tokens
    /// @param addr The address holding the new token
    /// @param value The amount of token to be minted
    /// @dev This function performed no check on the caller. Must stay internal
    function _mint(address addr, uint value) internal{
        balances[addr] += value;
        require(balances[addr] >= value);
        emit Mint(addr, value);
    }

    /// @notice Mint tokens. Callable only by the owner
    /// @param addr The address holding the new token
    /// @param value The amount of token to be minted
    function mint(address addr, uint value) public onlyOwner{
        _mint(addr, value);
    }

    /// @notice Mint tokens. Used by the owner to mint directly tokens to himself. Callable only by the owner
    /// @param value The amount of token to be minted
    function mint(uint value) public{
        _mint(msg.sender, value);
    }

    /// @notice Return the user's balance
    /// @param dst User address
    function balanceOf(address dst) public returns(uint){
        return balances[msg.sender];
    }

}