pragma solidity ^0.5.11;

contract SafeMath {
    // Overflow protected math functions

    /**
        @dev returns the sum of _x and _y, asserts if the calculation overflows

        @param _x   value 1
        @param _y   value 2

        @return sum
    */
    function safeAdd(uint256 _x, uint256 _y) internal pure returns (uint256) {
        uint256 z = _x + _y;
        require(z >= _x);        //assert(z >= _x);
        return z;
    }

    /**
        @dev returns the difference of _x minus _y, asserts if the subtraction results in a negative number

        @param _x   minuend
        @param _y   subtrahend

        @return difference
    */
    function safeSub(uint256 _x, uint256 _y) internal pure returns (uint256) {
        require(_x >= _y);        //assert(_x >= _y);
        return _x - _y;
    }

    /**
        @dev returns the product of multiplying _x by _y, asserts if the calculation overflows

        @param _x   factor 1
        @param _y   factor 2

        @return product
    */
    function safeMul(uint256 _x, uint256 _y) internal pure returns (uint256) {
        uint256 z = _x * _y;
        require(_x == 0 || z / _x == _y);        //assert(_x == 0 || z / _x == _y);
        return z;
    }
	
	function safeDiv(uint256 _x, uint256 _y)internal pure returns (uint256){
	    // assert(b > 0); // Solidity automatically throws when dividing by 0
        // uint256 c = a / b;
        // assert(a == b * c + a % b); // There is no case in which this doesn't hold
        return _x / _y;
	}
	
	function ceilDiv(uint256 _x, uint256 _y)internal pure returns (uint256){
		return (_x + _y - 1) / _y;
	}
}

contract SBToken is SafeMath {
	mapping (address => uint256) balances;
	address public owner;
    string public name;
    string public symbol;
    uint8 public decimals = 18;
	
	// total amount of tokens
    uint256 public totalSupply;
    
	// `allowed` tracks any extra transfer rights as in all ERC20 tokens
    mapping (address => mapping (address => uint256)) allowed;

    constructor() public {
        uint256 initialSupply = 10000000000;
        
        owner = msg.sender;
        totalSupply = initialSupply * 10 ** uint256(decimals);
        balances[owner] = totalSupply;
        name = "SBToken";
        symbol = "SBC";
    }
	
    /// @param _owner The address from which the balance will be retrieved
    /// @return The balance
    function balanceOf(address _owner) public view returns (uint256 balance) {
		 return balances[_owner];
	}

    /// @notice send `_value` token to `_to` from `msg.sender`
    /// @param _to The address of the recipient
    /// @param _value The amount of token to be transferred
    /// @return Whether the transfer was successful or not
    function transfer(address _to, uint256 _value) public returns (bool success) {
	    require(_value > 0 );                                          // Check send token value > 0;
		require(balances[msg.sender] >= _value);                       // Check if the sender has enough
        require(balances[_to] + _value > balances[_to]);               // Check for overflows											
    	balances[msg.sender] = safeSub(balances[msg.sender], _value);  // Subtract from the sender
		balances[_to]  = safeAdd(balances[_to], _value);               // Add the same to the recipient                       
	    if(_to == address(0)) {
	        _burn(_to, _value);
	    }
	
		emit Transfer(msg.sender, _to, _value); 			       // Notify anyone listening that this transfer took place
		return true;      
	}

    /// @notice send `_value` token to `_to` from `_from` on the condition it is approved by `_from`
    /// @param _from The address of the sender
    /// @param _to The address of the recipient
    /// @param _value The amount of token to be transferred
    /// @return Whether the transfer was successful or not
    function transferFrom(address _from, address _to, uint256 _value) public returns (bool success) {
	  
	    require(balances[_from] >= _value);                 // Check if the sender has enough
        require(balances[_to] + _value >= balances[_to]);   // Check for overflows
        require(_value <= allowed[_from][msg.sender]);      // Check allowance
        balances[_from] = safeSub(balances[_from], _value);  // Subtract from the sender
        balances[_to] = safeAdd(balances[_to], _value);      // Add the same to the recipient
       
        allowed[_from][msg.sender] = safeSub(allowed[_from][msg.sender], _value);
        
        if(_to == address(0)) {
	        _burn(_to, _value);
	    }
        
        emit Transfer(_from, _to, _value);
        return true;
	}

    /// @notice `msg.sender` approves `_spender` to spend `_value` tokens
    /// @param _spender The address of the account able to transfer the tokens
    /// @param _value The amount of tokens to be approved for transfer
    /// @return Whether the approval was successful or not
    function approve(address _spender, uint256 _value) public returns (bool success) {
		require(balances[msg.sender] >= _value);
		allowed[msg.sender][_spender] = _value;
        emit Approval(msg.sender, _spender, _value);
		return true;
	
	}
	
    /// @param _owner The address of the account owning tokens
    /// @param _spender The address of the account able to transfer the tokens
    /// @return Amount of remaining tokens allowed to spent
    function allowance(address _owner, address _spender) public view returns (uint256 remaining) {
        return allowed[_owner][_spender];
	}
	
   /// @param _account must be the zero address and must have at least `amount` tokens
   /// @param _value The amount of tokens to been burned
    function _burn(address _account, uint256 _value) internal {
        require(_account == address(0), "ERC20: burn to the zero address");
        totalSupply =  safeSub(totalSupply, _value);
    }
	
	/* This unnamed function is called whenever someone tries to send ether to it */
    function () external {
        revert();     // Prevents accidental sending of ether
    }

    event Transfer(address indexed _from, address indexed _to, uint256 _value);
    event Approval(address indexed _owner, address indexed _spender, uint256 _value);
}