smart contracts

先来一段合约代码：
// MetaCoin.sol 用于账户转账的智能合约应用
contract MetaCoin {
    mapping (address => uint) balances;
    function MetaCoin() {
       balances[tx.origin] = 10000;
    }
    function sendCoin(address receiver, uint amount) returns(bool sufficient) {
        if (balances[msg.sender] < amount) return false;
        balances[msg.sender] -= amount;
        balances[receiver] += amount;
        return true;
    }
   function getBalance(address addr) returns(uint) {
        return balances[addr];
    }
}