Why is it not possible to reassign the value in the contract level in solidity?

Question

This is my code, I want to know the reason why I am not able to change the value in the variable a. Would you please give me the reason or any information from solidity doc?

// SPDX-License-Identifier: MIT
pragma solidity >=0.8.0 <0.9.0;

contract simple {
    uint public a = 3;
    a = 16; // error occurred : parser Error expected identifier but got '='
    }

Answer 1

You are trying to change the data in the declarative part of the contract code. Put the change in the contract constructor or function.

// SPDX-License-Identifier: MIT
pragma solidity >=0.8.0 <0.9.0;

contract simple
{
    uint public a = 3;

    constructor()
    {
      a = 16; 
    }

    function changeData() public
    {
      a = 16;
    }

}