Mastering Blockchain Programming with Solidity

Avoid adding new variables before existing variables

You should not add a new state variable before any of the existing state variables present in the contract:

//Bad Practicecontract SampleContract {    uint256 public x;    uint8 public decimals;  //Added new variable in between    string public y;}

In the preceding code, between the x and y variables, a new variable, decimals, has been added. This should be avoided.