자판기 스마트 컨트랙트 개발

⚠️ If the license identifier isn’t included in the contract file the compiler will now show a warning.

❗ If there are multiple license identifiers in the contract file the compiler will now show an error.

We now need to write the version of solidity that we are going to be using:

pragma solidity ^0.8.15;

The next step is to create a contract. In Solidity, we write a smart contract by typing the keyword contract followed by the name of the contract. Let us proceed by naming our contract Vending Machine. So, write:

contract VendingMachine{

        }

We will write our further code in the curly brackets as all the functions and variables would be a part of it. Next, we define the variables that will be a part of the contract that is:

1: Address public owner;
2: mapping(address => uint) public lizyBalances;

Here, address refers to the wallet address of the owner and mapping refers to a keyword where we can map one type of variable to be associated with another.

So, lizyBalances is a mapping where number of lizy's will be associated with the address. Next, we go on to create a constructor that will be automatically executed when deployment will occur on the Ethereum Blockchain.

 constructor(){
            owner = msg.sender;
            lizyBalances[address(this)] = 1000;
            }

The creation of first function is getBalance(). It is used to get the balance of lizy's that are left in the Vending Machine.

lizyBalances[address(this)] represents the balance of the lizy's that are associated with the current Ethereum account.

            function getBalance() public view returns (uint) {

                return lizyBalances[address(this)];

                }

Function that is next is called restock(). It is restricted only to the owner and thus, the keyword comes as require.
The lizyBalances gets updated when the amount is entered by the owner to be incremented.

        function restock(uint amount) public {

            require(msg.sender == owner, "Only owner can restock the lizy!");
            lizyBalances[address(this)]+= amount;

            }

The last function is the purchase function that actually helps the person or the customer to purchase a lizy's.

The price for one lizy's that we entered is 0.5 ETH. Thus, the msg.value should be equal to the amount multiplied by 0.5 ETH.

Also, the Vending machine should have the number of lizy's entered by the customer. When both of these requirements are fulfilled, then the lizyBalances of this address gets deducted by the amount.

Also, the msg.sender’s lizyBalances will get updated by the number of lizy's purchased.

            function purchase(uint amount) public payable{

                require(msg.value >= amount * 0.5 ether, "You must pay at least 0.5 ether per lizy");

                require(lizyBalances[address(this)] >= amount, "OOPS! Not enough lizy");

                lizyBalances[address(this)] -= amount;

                lizyBalances[address(msg.sender)] += amount;

                }

Finally, the code is done. Now we, proceed to compile it. The Remix automatically compiles the code and shows if there is some error or not. Then, we go ahead to Deploy the code.

To deploy our smart contract we are going to using the Injected Provider-Metamask environment.

Make sure that we are in Deploy and Run Transactions tab. Then the environment to be selected is Injected Provider-Metamask. The contract should be our Vending Machine contract.

Deploy it now, and you will get the deployed contract as follows. Also, now whenever the customer has purchased the lizy's, the lizyBalances gets updated when the function is called.