solidity加減乘除
===
//SPDX-License-Identifier： MIT
//版本要大於0.8.11
pragma solidity ^ 0.8.11;

//契約名稱叫做practice
contract practice{
int public answer = 10;
function Operator(string memory operation) public
{
if(keccak256(abi.encodePacked(operation)) ==keccak256(abi.encodePacked("add")))
{
answer+=1; //若是輸入的字元跟ADD比較，相同就把answer+1;
}
if(keccak256(abi.encodePacked(operation)) ==keccak256(abi.encodePacked("sub")))
{
answer-=1;//把輸入的字元跟sub比較，相同就是-1
}
}
function answer_double() view public returns(uint256)
{
return uint256(answer)*2; //把answer的數值乘以2
}
}