$ solc --bin -o ./contracts SimpleStore.sol Warning: This is a pre-release compiler version, please do not use it in product ion. SimpleStore.sol:1:1: Error: Source file requires different compiler version (cur rent compiler is 0.4.18-develop.2018.12.6+commit.9cf6e910.Linux.g++ - note that nightly builds are considered to be strictly less than the released version pragma solidity ^0.4.18;
it looks like you compiled a nightly commit, and the pragma requires the 0.4.18 version or later. You can use a later version of solidity, or use the release version
^0.4.18 means "0.4.18 or later", so you can simply use a later version, and that would be more secure. Just know that if you choose a 0.5.x version things may fail, since there where breaking changes, like going from function scoping to block scoping.