pragma solidity ^0.4.16;

interface tokenRecipient { 
    function receiveApproval (
        address _from, 
        uint256 _value, 
        address _token, 
        bytes _extraData
    ) public;
} 

contract KToken {
    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 Burn(address indexed from, uint256 value);
   
    function KToken(
        uint256 initialSupply, 
        string tokenName, 
        string 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 != 0x0);
        require(balanceOf[_from] >= _value);
        require(balanceOf[_to] + _value > balanceOf[_to]);
        uint previousBalances = balanceOf[_from] + balanceOf[_to];
        balanceOf[_from] -= _value;
        balanceOf[_to] += _value;
        Transfer(_from, _to, _value);
        assert(balanceOf[_from] + balanceOf[_to] == previousBalances);
     }
    
     function transfer(address _to, uint256 _value) public {
         _transfer(msg.sender, _to, _value);
     }

    function transferFrom(address _from, address _to, uint256 _value) public returns (bool success) {
        require(_value <= allowance[_from][msg.sender]);     
        _transfer(_from, _to, _value);
        return true;
    }

    function approve(address _spender, uint256 _value) public returns (bool success) {
        allowance[msg.sender][_spender] = _value;
        return true;
    }

    function approveAndCall(address _spender, uint256 _value, bytes _extraData) public returns (bool success) {
        tokenRecipient spender = tokenRecipient(_spender);
        if (approve(_spender, _value)) {
            spender.receiveApproval(msg.sender, _value, this, _extraData);
            return true;
        }
    }

    function burn(uint256 _value) public returns (bool success) {
        require(balanceOf[msg.sender] >= _value);   
        balanceOf[msg.sender] -= _value;                  
        totalSupply -= _value;                                       
        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;                             
        Burn(_from, _value);
        return true;
    }
}