demonstrating uint overflow and underflow in solidity

over_under.sol

/* demonstrating uint overflow and underflow in ethereum solidity
   this is why you need guards like: 
     if (balances[_to] + _amount < balances[_to]) throw; 
*/ 
contract C {
    // (2**256 - 1) + 1 = 0
    function overflow() returns (uint256 _overflow) {
        uint256 max = 2**256 - 1;
        return max + 1;
    }
    
    // 0 - 1 = 2**256 - 1
    function underflow() returns (uint256 _underflow) {
        uint256 min = 0;
        return min - 1;
    }
}