# Constants

Constant state used by the swap router

### State Variables <a href="#state-variables" id="state-variables"></a>

#### CONTRACT\_BALANCE <a href="#contract_balance" id="contract_balance"></a>

*Used for identifying cases when this contract's balance of a token is to be used*

```solidity
uint256 internal constant CONTRACT_BALANCE = 0;
```

#### MSG\_SENDER <a href="#msg_sender" id="msg_sender"></a>

*Used as a flag for identifying msg.sender, saves gas by sending more 0 bytes*

```solidity
address internal constant MSG_SENDER = address(1);
```

#### ADDRESS\_THIS <a href="#address_this" id="address_this"></a>

*Used as a flag for identifying address(this), saves gas by sending more 0 bytes*

```solidity
address internal constant ADDRESS_THIS = address(2);
```