address(0) can anyone explain me this?

[nikhil-b-more]

doing project on wallet but didnt getting why some of coders using this and actully what that code is perfoming.

[alymurtazamemon]

@0x-nikhilMore Where? I am not getting the context!

[krakxn]

The relevant code please

[nikhil-b-more]

// SPDX-License-Identifier:MIT

pragma solidity ^0.8.7;

contract MultiSigWallet{
event deposit(address sender, uint amount, uint time, uint balance );
event transactionProposal(address owner, address to, uint txIndex, uint amount);
event approveTransaction(address owner, uint txIndex);
event revokeTransaction(address owner, uint txIndex);
event executeTransaction(address owner, uint txIndex);

struct Transaction{
    uint time;
   
    address to;
    uint amount;
    uint numConfirmation;
    bool executed;
}

address[] public owners;
mapping(address => bool) public ownerDeclared;
uint numConfirmations;


Transaction[] public transactions;
mapping(uint =>mapping(address => bool)) public txConfirmed;

modifier isOwner(){
    require(!ownerDeclared[msg.sender], " Looks you are not owner of wallet ");
    _;
}
modifier isTxExist(uint _txIndex){
    require(_txIndex <= transactions.length, " transaction not exist");
    _;
}
modifier isConfirmed(uint _txIndex){
    require(!txConfirmed[_txIndex][msg.sender], "already executed");
    _;
}
modifier isExecuted(uint _txIndex){
    require(!transactions[_txIndex].executed, " transaction already placed and executed");
    _;
}


constructor(address[]memory _owners, uint _totoalConfirmationsRequired){
    
    require(_owners.length > 0, "minimum 1 owner required");
    require(_totoalConfirmationsRequired > 0 && _totoalConfirmationsRequired <= _owners.length, " please mention valid number fro confiramtion");

    for(uint256 i=0; i<_owners.length; i++){
       address owner = _owners[i];
    require(owner != address(0), "address repeated");
    require(!ownerDeclared[owner], " owner repeated");
    
    owners.push(owner);
    ownerDeclared[owner]= true;
    numConfirmations = _totoalConfirmationsRequired;
    }
}

function createTransaction( address _to, uint _amount) public isOwner{
    
   uint txIndex = transactions.length; 
    transactions.push(
        Transaction({
            time: block.timestamp,
            to: _to,
            amount: _amount,
            executed: false,
            numConfirmation: 0
        })
    );
     emit transactionProposal(msg.sender,_to, txIndex, _amount);
}

function confirmTransaction(uint _txIndex) public isOwner isTxExist(_txIndex) isExecuted(_txIndex) isConfirmed(_txIndex){
    Transaction storage transactionNum = transactions[_txIndex];

    transactionNum.numConfirmation += 1;
    transactionNum.executed = false;
    emit approveTransaction(msg.sender, _txIndex);
}

function revokTransaction(uint _txIndex) public isOwner isTxExist(_txIndex) isExecuted(_txIndex) isConfirmed(_txIndex){
    Transaction storage transactionNum = transactions[_txIndex];
    transactionNum.numConfirmation -= 1;
    transactionNum.executed = false;
    
    emit revokeTransaction(msg.sender, _txIndex);

}

function processTransaction(uint _txIndex) public isOwner isTxExist(_txIndex) isExecuted(_txIndex) isConfirmed(_txIndex){
    Transaction storage transactionNum = transactions[_txIndex];
    require(transactionNum.numConfirmation >= numConfirmations, "not having enough confirmations");
   (bool success, ) = transactionNum.to.call{value: transactionNum.amount}("");
   require(success, "tx failed");
   emit executeTransaction(msg.sender, _txIndex);

}

}

[nikhil-b-more]

line no. 55

[krakxn]

@0x-nikhilMore

require(owner != address(0), "address repeated");

As is the case here: an address is a hexadecimal value (a number in base 16), so address(0) converts the number 0 into an address type.

Further knowledge:

If the target account is the zero-account (the account with the address 0), the transaction creates a new contract. The address of that contract is not the zero address but an address derived from the sender and its number of transactions sent (the “nonce”). The payload of such a contract creation transaction is taken to be EVM bytecode and executed. The output of this execution is permanently stored as the code of the contract. This means that in order to create a contract, you do not send the actual code of the contract, but in fact code that returns that code.

Docs: If the target account is not set (the transaction does not have a
recipient or the recipient is set to null), the transaction creates a
new contract. As already mentioned, the address of that contract is
not the zero address but an address derived from the sender and its
number of transactions sent (the “nonce”).

address(0) is also called the "zero account", which is really just the fake account associated with the address 0x00000... and is a short way to write 0x0000000000000000000000000000000000000000 (which is essentially 0x0). The address is sometimes used to burn tokens, since it's very unlikely that someone has the private key for this address.