pragma solidity >=0.4.22 <0.6.0;

interface tokenRecipient { 
    function receiveApproval(address _from, uint256 _value, address _token, bytes calldata _extraData) external; 
}

contract TokenERC20 {
   
    string public name;
    string public symbol;
    uint8 public decimals = 18;
  
    uint256 public totalSupply;

  
    mapping (address => uint256) public balanceOf;
    mapping (address => mapping (address => uint256)) public allowance;

   
    event Transfer(address indexed from, address indexed to, uint256 value);
 
    event Approval(address indexed _owner, address indexed _spender, uint256 _value);

   
    event Burn(address indexed from, uint256 value);

  
    constructor(
        uint256 initialSupply,
        string memory tokenName,
        string memory tokenSymbol
    ) public {
        totalSupply = initialSupply * 10 ** uint256(decimals);  
        balanceOf[msg.sender] = totalSupply;               
        name = tokenName;                                   
        symbol = tokenSymbol;                               
    }

   
    function _transfer(address _from, address _to, uint _value) internal {
      
        require(_to != address(0x0));

        require(balanceOf[_from] >= _value);
        
        require(balanceOf[_to] + _value >= balanceOf[_to]);
       
        uint previousBalances = balanceOf[_from] + balanceOf[_to];
        
        balanceOf[_from] -= _value;
        
        balanceOf[_to] += _value;
        emit Transfer(_from, _to, _value);
       
        assert(balanceOf[_from] + balanceOf[_to] == previousBalances);
    }

   
    function transfer(address _to, uint256 _value) public returns (bool success) {
        _transfer(msg.sender, _to, _value);
        return true;
    }

   
    function transferFrom(address _from, address _to, uint256 _value) public returns (bool success) {
        require(_value <= allowance[_from][msg.sender]);    
        allowance[_from][msg.sender] -= _value;
        _transfer(_from, _to, _value);
        return true;
    }

   
    function approve(address _spender, uint256 _value) public
        returns (bool success) {
        allowance[msg.sender][_spender] = _value;
        emit Approval(msg.sender, _spender, _value);
        return true;
    }

   
    function approveAndCall(address _spender, uint256 _value, bytes memory _extraData)
        public
        returns (bool success) {
        tokenRecipient spender = tokenRecipient(_spender);
        if (approve(_spender, _value)) {
            spender.receiveApproval(msg.sender, _value, address(this), _extraData);
            return true;
        }
    }

   
    function burn(uint256 _value) public returns (bool success) {
        require(balanceOf[msg.sender] >= _value);   
        balanceOf[msg.sender] -= _value;           
        totalSupply -= _value;                      
        emit Burn(msg.sender, _value);
        return true;
    }

   
    function burnFrom(address _from, uint256 _value) public returns (bool success) {
        require(balanceOf[_from] >= _value);                
        require(_value <= allowance[_from][msg.sender]);    
        balanceOf[_from] -= _value;                         
        allowance[_from][msg.sender] -= _value;             
        totalSupply -= _value;                             
        emit Burn(_from, _value);
        return true;
    }
}