How to implement smart contract

Question

I am studying Smart Contract with solidity. I can't understand something, so I want to get expert advice.

I logged in to the Upbit exchange to trade the golem's token. The Upbit exchange gave me a token deposit address. That address was a contract address(0x27c6769A0549fa03DafEd89d555C7E71B21Dd35E)

After depositing the golem's token, something happened that I could not understand. There is no ether to pay for the gas at the deposit address, but the golem's token was transferred to another address.

Q1] To transfer tokens without Ether, how to implement smart contract?

Q2] If you know where to find the sample code to reference, I would like to know the url

Answer 1

Q1

There's no way to transfer anything without gas (Ether). Also as contracts can't do anything 'on their own' but someone has to initialize each action, most likely this is what happened:

1) You transfer tokens to the contract

2) The contract transfers them onwards somewhere

3) You pay for both transfers

Q2

For the code, I don't have a deployed version to show you but it could be something like this:

pragma solidity ^0.4.22;

contract GolemToken {
    function transfer(address to, uint tokens) public returns (bool success);
}

// 0x27c6769a0549fa03dafed89d555c7e71b21dd35e
contract ExchangeContract {

    function transfer(address to, uint tokens) public returns (bool success) {
        address golemTokenContract = 0x00;
        address forwardAddress = 0x01;
        GolemToken gt = GolemToken(golemTokenContract);
        // Instead of transferring to 'to', transfer elsewhere
        gt.transfer(forwardAddress, tokens);
    }
}