send/mint/transfer currency

currency.sol

// SPDX-License-Identifier: GPL-3.0

pragma solidity >=0.5.0 <0.9.0;
import "github/OpenZeppelin/openzeppelin-contracts/contracts/math/SafeMath.sol";

contract Scoin  { 
    using SafeMath for uint256;
    
    address public minter;
    mapping (address => uint256) public balances;
    
    event Sent(address indexed from , address indexed to, uint256 amount, uint256 sBalance, uint256 rBalance);
    event OwnerChanged(address indexed from , address indexed to);
    
    constructor() public {
        minter = msg.sender;
        emit OwnerChanged(address(0), minter);
    }
    
    
    modifier onlyOwner { 
        require(msg.sender == minter);
        _;
    }
    
    // only creator can mint the token
    function mint(address _receiver, uint256 _amount) public onlyOwner { 
        uint256 currentBalance =  balances[_receiver].add(_amount);
        require(currentBalance >= balances[_receiver], "out of bound");
        balances[_receiver] = currentBalance;
    }
    
    // send amount of  coins from any caller to an address
    function send(address _receiver, uint256 _amount) public {
        require(balances[msg.sender] >= _amount, "Insufficient balance");
         balances[msg.sender] = balances[msg.sender].sub(_amount);
         balances[_receiver] = balances[_receiver].add(_amount);
        emit Sent(msg.sender, _receiver, _amount, balances[msg.sender], balances[_receiver]);
    }
}