For/If Loop has no errors but does not push the value to the array - ethereum

Question

I am trying to create a whitelist. I've used a for and if loop to check if the msg.sender already exists in the array. When the whitelist() function is run, no errors are returned, but when I run check(), it tells me the address doesn't exist in the array, same thing with directing fetching the array.
//SPDX-License-Identifier: MIT
pragma solidity ^0.8.0;
contract SelfWhitelist {
address[] public addressWhitelist;
function whitelist() public returns(string memory) {
for(uint i = 0; i < addressWhitelist.length; i++) {
if(addressWhitelist[i] != msg.sender) {
addressWhitelist.push(msg.sender);
return "Whitelisted!";
}
}
return "Already whitelisted!";
}
function check() public view returns (bool){
for(uint i = 0; i < addressWhitelist.length; i++){
if(addressWhitelist[i] == msg.sender)
return true;
}
return false;
}
}
I added this block of code to check for duplicate entries in the array.
for(uint i = 0; i < addressWhitelist.length; i++) {
if(addressWhitelist[i] != msg.sender) {
addressWhitelist.push(msg.sender);
return "Whitelisted!";
}
Expected for no errors and my address being pushed to the array.
The code ran without errors, but nothing was added to the array.

Answer 1

I would use mapping type to hold the whitelisted addresses, then you don't have to loop over the array
contract SelfWhitelist {
mapping(address => bool) public addressWhitelist;
function whitelist() public returns(string memory) {
if (check()) {
return "Already whitelisted!";
}
addressWhitelist[msg.sender] = true;
return "Whitelisted!";
}
function check() public view returns (bool) {
return addressWhitelist[msg.sender];
}
}
And in your code, seems you have logical issues:
for(uint i = 0; i < addressWhitelist.length; i++) {
if(addressWhitelist[i] != msg.sender) {
addressWhitelist.push(msg.sender);
return "Whitelisted!";
}
}
if the array is empty, the loop never executes, so nothing will be added
if the first item is not msg.sender, msg.sender will be whitelisted, even though it might be already whitelisted.