pragma solidity ^0.4.24;

contract MemoryAndStorage {
    uint[20] public arr; // storage value by default
    
    function startChange() public {
        firstChange(arr);
        secondChange(arr);
    }
    
    function firstChange(uint[20] storage x) internal {
        x[0] = 4;
    }
    
    function secondChange(uint[20] x) internal pure{ // argument in function is a memory value by
        x[0] = 3;                                // by default 
    }
    
}