In this chapter, we will learn how to deploy contract on Ethereum. Click on the Run menu option to deploy the contract. The following screen will appear. The contract name is shown in the highlighted list box. Below this, you will notice the Deploy button, click on it to deploy the contract. The contract will be deployed on the Remix built-in Blockchain. You will be able to see the deployed contract at the bottom of the screen. You can see this in the highlighted portion of the screenshot below. Notice, the presence of three method names in this highlighted region. Next, you will interact with the contract by executing the contract methods.
Compiling the Contract
Once you write the complete contract code, compiling it in this IDE is trivial. Simply click on the Autocompile checkbox in the IDE as shown in the screenshot below − Alternatively, you may compile the contract by clicking the button with the title “Start to compile”. If there is any typo, fix it in the code window. Make sure the code is compiled fully without errors. Now, you are ready to deploy the contract.
Developing MyContract
We will name our contract MyContract as in the following declaration − We will declare two variables as follows − The variable amount will hold the accumulated money sent by the contract executors to the contract creator. The value field will hold the contract value. As the executors execute the contract, the value field will be modified to reflect the balanced contract value. In the contract constructor, we set the values of these two variables. As initially, the amount collected on the contract is zero, we set the amount field to 0. We set the contract value to some arbitrary number, in this case it is 1000. The contract creator decides this value. To examine the collected amount at any given point of time, we provide a public contract method called getAmount defined as follows − To get the balanced contract value at any given point of time, we define getBalance method as follows − Finally, we write a contract method (Send). It enables the clients to send some money to the contract creator − The execution of the send method will modify both value and amount fields of the contract. The complete contract code is given below −
Solidity for Contract Writing
Solidity is an object-oriented language especially developed for contract writing. It is a high-level language, which inherits traits from C++, Python, and JavaScript. The Solidity compiler compiles your source code into bytecode that runs on Ethereum Virtual Machine (EVM). For quick understanding of the Solidity syntax, look at the sample code in the IDE. pragma solidity >=0.4.22 <0.6.0; contract Ballot { The first line is a directive to the compiler. The second line starts the definition of the contract. Within the contract, you declare variables such as − address chairperson; You can also define structures such as Proposal and create an array of these structure items. Examine this in the code window. You may then define a constructor which is invoked at the time of instantiating a contract. constructor(uint8 _numProposals) public { After the constructor, you will define several methods, which are the contract methods. In the sample contract, giveRightToVote is one such method having the following syntax − function giveRightToVote(address toVoter) public { The public keyword makes this method publicly invokable by any client who has access to the contract. Likewise, the sample contract defines three more methods called delegate, vote, and winningProposal. Examine these for your own understanding of the Solidity syntax. These are the prerequisites to writing your own contract. Explaining the full syntax of Solidity is beyond the scope of this tutorial.
Smart Contracts
There are several tools available to develop and test contracts. One of the simplest tools is provided on the official Ethereum site itself. The tool is called Remix, we will use this for our contract development. Remix for Contract Development Open the Remix IDE by typing in the following URL in your browser.https://remix.ethereum.org The following screen will appear. In the center window, you will see some default code, which is a sample Solidity code. You will type your contract code in this code editor. Your code may be auto-compiled. Upon successful compilation of the code, you will be able to run the code in the same IDE. When you execute the contract methods, the results will be displayed in the same IDE window. There are facilities to debug the code and to unit test your project. These can be seen in the menu bar at the top right hand side as shown in the IDE screenshot below. You will be using these options shortly. You will now start writing your contract.
Introduction
A huge success of Bitcoin raised interest in the minds of several to create their own currencies. Looking at the advantages offered by Bitcoin – a digital currency, people wanted to use the concept of Blockchain in their own applications. People wanted to move out of their physical contracts to smart digital contracts where several issues like repudiation, transparency, security, etc. would be automatically addressed. The outcome of this effort resulted in the creation of Ethereum – a popular platform for creating distributed Blockchain applications that support smart contracts. In this tutorial, you will learn how to create a distributed application (DAPP) on Ethereum platform. More specifically, you will learn how to write a contract, test it on a local Blockchain and finally deploy it on an external Blockchain for deep testing and commercial use. You will use Solidity, an object-oriented language for contract development. You will also use Remix, an open source IDE for developing and testing contracts. To deploy the tested contract on an external Blockchain, you will use Ganache. To interact with the contract you will need a client application. We will use MyEtherWallet to create a wallet for each such client. The contract creator will publish the contract. Any other client will look at the contact value by using the interface provided by the contract and send some money to the creator for executing a part of the contract. So let us begin by writing the contract.
Ethereum Tutorial
Looking at the advantages offered by Bitcoin − a digital currency, people wanted to use the concept of Blockchain in their own applications. People wanted to move out of their physical contracts to smart digital contracts where several issues like repudiation, transparency, security, etc. would be automatically addressed. The outcome of this effort resulted in the creation of Ethereum − a popular platform for creating distributed Blockchain applications that support smart contracts. Audience This tutorial is designed for those who wish to gain some insight on how Ethereum works. After completing this tutorial, you will find yourself at a moderate level of expertise from where you can take yourself to the next level. Prerequisites Before proceeding with this course, we assume the reader has basic understanding in Web Development, JavaScript, Ajax-Requests, AngularJS, Gulp/Grunt and the Node Package Manager.
Future
Since Bitcoin is a new emerging technology which is underway, unforeseen developments can make its existence and continuation difficult. Concerning its security and future, there are numerous questions which no one can answer. How far can we trust Bitcoins? Are they a bubble that is going to burst? Are they a passing phenomenon and a fad that would fizzle out over a period of time? Or are they going to stay put and perhaps dominate other currencies in future? As of now, bitcoins are mostly unregulated, however this may change. Governments are worried about losing taxes and control over the currency. They may bring legislations to regulate bitcoin which may hugely impact the advantages that bitcoins have over other currencies. The volatility of bitcoin prices is one huge issue. The wild fluctuations in its index is sign of such volatility. In recent years, bitcoin prices have risen exponentially and after some corrections have dipped but still they are on the high side. Many expect that the price will further increase. Favoring Growth Factors The things that favor the growth of bitcoin adoption are as follows − Next halving is scheduled to occur in 2020. This will further decrease the rate of supply of bitcoins while bitcoin usage would have increased manifold by 2020. As of now, the number of bitcoin transactions is way behind the number of credit card transactions and the former has to significantly increase to realize the full potential of bitcoins. Some of the issues which have to be tackled to help bitcoin’s growth are as follows − Governments of several countries including India are discouraging legal use of Bitcoins as they understand that Bitcoin is a parallel financial system beyond their control. However, countries like Japan, Australia and several European countries have made Bitcoin legal as they realized that they cannot stop the usage of bitcoins. Some countries have banned bitcoin exchanges. People are using global exchanges to hide their transactions. Meanwhile India and China have been discouraging Bitcoin transactions. China has tried to ban all Bitcoin Exchanges in their country while India has not banned any exchange. Zebpay and Unocoin are Bitcoin Exchanges that are under operation in India. They require submission of KYC documents before executing any Buy or Sell transaction.
Applications
The following is a list of applications of bitcoins
Glossary
In this chapter, we shall learn bitcoin glossary which describes over 50 bitcoin terms. Address A bitcoin address allows us to send and receive bitcoins on the bitcoin network. It is also the public key or address that is used to transact in bitcoins. Altcoin Altcoin is a group of ‘alternate’ cryptocurrencies other than bitcoins. Examples of altcoins include Ethereum, Litecoin and PPcoin. Explore our latest online courses and learn new skills at your own pace. Enroll and become a certified expert to boost your career. Asic An Application Specific Integrated Circuit (ASIC) is built specially to process the SHA- 256 hashing equations that are used in mining bitcoins. Asic miner An ASIC miner is the latest mining hardware used in bitcoin mining. It is used to calculate the SHA-256 equation faster than a CPU or a GPU. ASIC miners are custom-built and connect to the network through a wireless or Ethernet connection. Bitcoin Price Index (BPI) The Bitcoin Price Index, designed by Coin Desk, shows the average bitcoin prices across the top global currency exchanges. Bitcoin Whitepaper The Bitcoin Whitepaper dubbed as the Bible of the Bitcoin ecosystem, was submitted by the currency’s mysterious founder, Satoshi Nakamoto, in 2008. It gives a detailed description of the bitcoin protocol, and is a good reference material for newbies and experienced people alike. Block Chain This chain contains the records of all bitcoin ‘blocks’ that have been mined since the start of the currency. The chain is designed such that each block contains the hash of the preceding block, which makes the chain secure against counterfeit mining operations. Block Reward A reward is given to each miner who completes a transaction block. It can be in the form of coins or transaction fees; Bitcoin network currently rewards 25 coins for each completed block. Once the threshold of blocks has been mined (which currently stands at 210,000 blocks) the reward is halved; such an event as described above is called halving. The next halving is due to take place in 2020. Then the reward would become 12.5 coins for mining one block. BTC BTC is the abbreviation of bitcoin, similar to USD and GBP for US dollar and Great. Bitcoin Client This is the software program that connects a device, whether a desktop computer, laptop or mobile phone to the bitcoin network. Confirmation A confirmation of a transaction is its successful hashing into the block of a blockchain. It can take up to ten minutes, though larger transactions may require up to 6 confirmations. Coloured Coins Coloured coins is a proposed new feature of bitcoins that allows users to define their own attributes of the currency. It is intended that users could mark a bitcoin as a physical asset, which could then be exchanged as a token for other property. Coinbase The name of a bitcoin wallet operator that offers payment processing for merchants, and acts as an intermediary in bitcoin exchanges. Coin Age A coin’s age is calculated by the product of the currency amount and the period of time it has been owned. Cryptocurrency A cryptocurrency is considered legal tender by consensus and is secured by using cryptography based on mathematical formulas. Cryptography It is the field where math formulas and algorithms are used to create the codes that encrypt and decrypt information. Double Spending This is the criminal act of spending the same bitcoins more than once. The user completes a transaction using his bitcoins and then makes a second transaction with some other party using the same bitcoins. So confirmation is necessary to validate a transaction and prevent double spend. So zero-confirmation transactions are risky as they could involve double spending. Dust Transaction This is a transaction that has a record in the block chain but has very little worth. Steps are being taken to minimise the number of dust transactions that take place by introducing a minimum transaction amount. ECDSA ECDSA is the name of a code and an abbreviation for Elliptic Curve Digital Signature Algorithm. It is used in the Bitcoin protocol to sign transactions. Escrow An escrow is a kind of third party online wallet that stores funds securely during a transaction between two parties. It is used in cases where two parties cannot transact bitcoins till certain conditions are met, and want to ensure that their money is not ‘stolen’ digitally. Faucet A faucet is the method of mining a certain number of coins when launching a new cryptocurrency, and then giving these away in order to promote interest in the new currency. There are several bitcoin faucet sites that give away very small amounts of bitcoins to promote them Fiat Currency A Fiat currency is another name for token money used across the world that has been declared legal tender by governments and central banks and is not backed by a physical commodity. Fork A fork in a blockchain is said to occur when one group of miners starts hashing a different set of transaction blocks. It can also happen when a new version of the bitcoin client is introduced. A fork is deemed successful if it becomes the longer version of the chain. Genesis Block The original block in a chain. GPU This is a graphical processing unit, as found in standard PC graphics card. As GPUs are designed to process huge data at faster speeds in pixel-heavy computer games, they are also perfect for processing calculations required in cryptocurrency mining. Hash A hash is the mathematical processing done during bitcoin mining. It is a complex process that makes the currency secure and renders decryption very difficult and alteration of the output detectable. Hash Rate Hash rate counts the number of hash calculations done in a second. This generally indicates how fast and successful a mining operation is. Input Input shows where a bitcoin transaction has originated, and is generally a bitcoin address, unless it is a generation transaction meaning that the bitcoin has been newly-mined. Litecoin It is a type of alternate crypto currency that uses