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It's available for purchase on LeanPub. If you are interested in learning more about Smart Contracts and building Decentralized apps, feel free to give this a try. If you are looking for advanced stuff such as Presale, Public Sale, Discounts, goal, hard cap etc.. Lately I have been digging into blockchain and decentralised apps to educate myself and improve my knowledge. This article aims to give you an overview of how smart contracts work in Ethereum by launching a simple demo ICO.

Make Hashnode your discussion hub for all things crypto. Check out our crypto communities and join the blockchain-related discussions. Here are a few basic terms we are going to use in this article. If you are familiar with the following concepts, feel free to skip to the next section.

You can create your own crypto-currencies based on Ethereum. Additionally the benefit of following ERC20 standard is that your tokens will be compatible with any other client or wallets that use the same standards. Smart Contracts: Smart Contracts are self executing code blocks deployed on the Ethereum blockchain. Contracts make decisions, interact with other contracts, store data and transfer Ether the unit of crypto-currency in the Ethereum blockchain among users.

Based on the original source from Token-Factory. The above code uses Solidity language to build a simple ERC20 token. The code is well commented and is very easy to understand. This is what you need to change based on the characteristics of your token. The total supply is capped at , but people can possess as little as 0. Additionally, the owner of the contract one who executes it gets all the initial tokens.

I have set the ICO price as following:. Download MetaMask chrome extension to generate a wallet. This is going to be the owner of the smart contract. Alternatively you can always use Mist or My Ether Wallet. For the sake of simplicity let's use MetaMask extension in this project. Once you download the extension, go ahead and create a new account protected by a password.

Then choose "Ropsten TestNet" from the top left corner. Before we deploy the contract to Main Ethereum blockchain, we'll test it against TestNet and make sure everything works as expected. It looks something like this:. Now head over to Remix IDE an online solidity compiler and debugger and paste the code you just modified. Ignore any warnings you see.

Next go to settings and uncheck "Enable Optimizations" if it's checked. Once you hit create, MetaMask will prompt you to buy some test ether and submit the transaction. Now open up MetaMask again and click on the first transaction. It'll take you to Etherscan where you can observe the ongoing transaction. It may take up to 30s to confirm the transaction.

Once it's confirmed it looks like the following:. You just deployed your contract. Note the to address in the above transaction page. That's your contract address. Ideally if you've set up everything correctly you should receive all the initial tokens in my case when you add it to your wallet.

It looks like the following:. Hit Add and refresh MetaMask. You should now see all the initial supply in my case it was HTCN. Now that everything works perfectly we just have to verify our smart contract so that everyone on the blockchain can read and understand it. It's always a good practice to verify since it helps establish trust. How do we set the number of ICO tokens? Well, there are a number of ways of setting the maximal number of ICO tokens and this matter might be worth a lengthy discussion by itself.

A constructor is a special function automatically called by Ethereum right after the contract is deployed. It contains important data for performing the contract. The field we are using here: msg. This function will return the number of all tokens allocated by this contract regardless of owner. The transferring owner is msg. In this case that the transferring account has a sufficient balance to execute the transfer. If a require statement fails, the transaction is immediately rolled back with no changes written into the blockchain.

Right before exiting, the function fires ERC20 event Transfer allowing registered listeners to react to its completion. What approve does is to allow an owner i. As you can see, this function is used for scenarios where owners are offering tokens on a marketplace. It allows the marketplace to finalize the transaction without waiting for prior approval.

This function returns the current approved number of tokens by an owner to a specific delegate, as set in the approve function. The transferFrom function is the peer of the approve function, which we discussed previously. It allows a delegate approved for withdrawal to transfer owner funds to a third-party account.

The two require statements at function start are to verify that the transaction is legitimate, i. This basically allows a delegate with a given allowance to break it into several separate withdrawals, which is typical marketplace behavior. We could stop here and have a valid ERC20 implementation. However, we want to go a step further, as we want an industrial strength token. This requires us to make our code a bit more secure, though we will still be able to keep the token relatively simple, if not basic.

SafeMath is a Solidity library aimed at dealing with one way hackers have been known to break contracts: integer overflow attack. In such an attack, the hacker forces the contract to use incorrect numeric values by passing parameters that will take the relevant integers past their maximal values.

SafeMath protects against this by testing for overflow before performing the arithmetic action, thus removing the danger of overflow attack. The library is so small that the impact on contract size is minimal, incurring no performance and little storage cost penalties. SafeMath uses assert statements to verify the correctness of the passed parameters.

Should assert fail, the function execution will be immediately stopped and all blockchain changes shall be rolled back. The name and symbol fields can be changed at will. Most tokens keep the decimal value at 18, so we will do the same.

The time has come to deploy our contract to the blockchain. Following deployment, our contract will be transferred to all nodes participating in the network. Any and all changes made to the contract will be propagated to all participating nodes. Ethereum developers usually employ deployment tools such as Truffle. Even Truffle is overkill for the limited needs of this article, and a simple online tool called Remix will suffice. To use it, you will need to install the MetaMask plugin on your browser and a Rinkeby Ethereum test network account with at least some Rinkeby Ether in it.

Now that we have all the building blocks in place, we will head over to Remix and paste the code above, including the pragma line and the SafeMath library, into the online editor. You have just deployed your first ERC20 token, like a true Ethereum professional. As promised, the token is simple and lightweight, yet fully functional, ERC20 standard compliant, and secured with MathSafe. It is ready to be purchased, paid with, and transferred throughout the Blockchain.

No, not even close, as our brief demonstration barely scratches the surface and deals solely with one aspect of smart contract development. Smart contracts can be much more complex depending on your business logic, your modeling of the user interaction, whether or not you allow token minting and burning, lifecycle changes you introduce into the contract, the need for admin-level capabilities which usually comes with an admin-authorized set of functions, and so on.

You get the picture. Still, if you can replicate what we did here, that is a solid foundation to expand your knowledge and move on to more complex contracts when necessary. A smart contract is a piece of code executed on the Ethereum Virtual Machine.

An Ethereum smart contract is immutable and can send or receive ether and data. Operations handled by these contracts include getting the total supply and balance of tokens, and the methods used to transfer them. The number 20 is assigned to this request, hence the suffix. Subscription implies consent to our privacy policy.