How can resolve 'Undeclared identifier' during withdraw from smart contract?

Question

I created an array of each address and amount of all users who have previously deposited a certain amount of ETH, then used the 'transfer' function (within : retireMyCoins()) to retrieve the amount and address of the user who is using the contract from the list. The user can then withdraw his ETH.

When compiling the contract, in the last function "retireMyCoins" the console returns the following error: 'Undeclared identifier'.

pragma solidity ^0.4.17;

contract myVault {
                     
    address[] public users;                      
    uint[] public totalDeposited;                

    function sendToken(address user, uint amount) public payable {
        require(msg.value > 0.001 ether);      
        
        user = msg.sender;                      
        amount = msg.value;  

        users.push(msg.sender);                 
        totalDeposited.push(msg.value);        

    }

    function getUsers() public view returns (address[]) {    
        return users;
    }

    function getAmount() public view returns (uint[]) {
        return totalDeposited;
    }

    function retireMyCoins() public {
        require(user[msg.sender]); 
        require(amount[msg.value]); 
        user.transfer(this.amount); 
    }
}

Answer 1

You have to create amount as a store variable in the beginning of your contract. Also, to make it work as you expect, you should map the balance of each user, like the following:

...
mapping( address => uint ) balances;
function sendToken(address user, uint amount) public payable {
    balances[msg.sender] = amount;
...
}

and then you can allow the withdrawal:

function retireMyCoins() public {
   uint amountToWithdraw = balances[msg.sender]
   balances[msg.sender] = 0; 
   msg.sender.transfer(amountToWithdraw); 
}

Remember to zero the user balance before the transfer as above.