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contracts...StorageArrayTest.sol

// SPDX-License-Identifier: GPL-3.0
pragma solidity ^0.8.17;

contract StorageArrayTest {
    uint256[] bigArray;
   
   
    // the bigArray's slot store the length of the bigArray. The initial value is zero. Firstly, the default value is zero.
    function testFixedArrayLength() external view returns(uint) {
        return  bigArray.length;

    }

    
    function pushTest(uint num) external  {
        bigArray.push(num);
    }

    // 1. each time, should check the array's lengh. if equal 0, just revert.  ZeroArray
    // 2. after each pop, should update the array's length
    function popTest() external  {
        bigArray.pop();
    }

    // no matter read or write, Firstly should check the index is in the range of lenght. index is beginning from zero 


    // just based on the bigArray's storage mechniams, get the corrospending value.
    
    /**
    function readBigArrayLocation(uint256 index)
        external
        view
        returns (uint256 ret)
    {
        uint256 slot;
        assembly {
            slot := bigArray.slot
        }
        bytes32 location = keccak256(abi.encode(slot));

        assembly {
            ret := sload(add(location, index))
        }
    }
    based on desgin, read and update the value.
    https://github.com/RareSkills/Udemy-Yul-Code/blob/17aec03882dd951b0d15707d71b6ab38626d853c/Video-06-Storage-3.sol#L41
        
    **/
    function readTest(uint index) external view returns (uint) {
        return bigArray[index];
    }

    function writeTest(uint index,uint new_num) external {
         bigArray[index] = new_num;
    }

    
    
}