{"componentChunkName":"component---src-templates-tag-js","path":"/tags/blockchain/","result":{"data":{"site":{"siteMetadata":{"title":"LoginRadius Blog"}},"allMarkdownRemark":{"totalCount":2,"edges":[{"node":{"fields":{"slug":"/engineering/guest-post/ethereum-smart-contract-tutorial/"},"html":"

What is a Smart Contract?

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Smart Contracts 📝 are simple programs stored on a blockchain network.

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You can say it's like an agreement between two people in the form of computer code. The transactions in a smart contract are processed by the blockchain and stored as a 42 character hex address with the prefix \"0x\"). All of which means that they can be sent automatically without needing a third party.

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🤔 Remember: They're stored in a public database. And once a smart contract is deployed, it cannot be changed.

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What is Solidity?

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Solidity is one of the most popular languages used for building smart contracts on Ethereum Blockchain. It's also an object-oriented programming language.

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Build Your First Smart Contract

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    \n
  1. Open Remix IDE from here.
    2. \n
  2. Click on Sure and then Done.
    3. \n
  3. Under default_workshop, click on create new file.
    4. \n
  4. Rename it as Hostel.sol.
    5. \n
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Now you're ready to write your first Smart Contract. 🤩

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Contract Code

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    \n
  1. You have to provide the solidity version in the smart contract:
    2. \n
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pragma solidity ^0.5.16;
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    \n
  1. Now create the main contract named Hostel:
    2. \n
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contract Hostel{\n    ...\n}
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    \n
  1. Now, inside the contract Hostel{...} follow the steps below.
    2. \n
  2. Create some variables where the smart contract will store the payable address (42 char hex string with prefix : \"0x\") of the Landlord & the Tenant.
    3. \n
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    address payable tenant;\n    address payable landlord;
\n
    \n
  1. Create some public variables where the smart contract will store some integer values. For this, there's a data type called uint (256-bit unsigned integer)
    2. \n
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    uint public no_of_rooms = 0;\n    uint public no_of_agreement = 0;\n    uint public no_of_rent = 0;
\n
    \n
  1. Now, create a structure to store details of each Hostel room like Hostel no., Hostel name, Hostel address, No of total agreements, Monthly rent, One-time security deposit, Last agreement sign time, Vacancy, Landlord address, and Current Tenant Address.
    2. \n
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    struct Room{\n        uint roomid;\n        uint agreementid;\n        string roomname;\n        string roomaddress;\n        uint rent_per_month;\n        uint securityDeposit;\n        uint timestamp;\n        bool vacant;\n        address payable landlord;\n        address payable currentTenant;\n    }
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    \n
  1. map previous structure with a uint(named : roomid).
    2. \n
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mapping(uint => Room) public Room_by_No;
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    \n
  1. Similar to the above, create a structure for each Rental Agreement and map that with a uint(named: agreementid). This will store details like: Hostel no., Agreement No, Hostel name, Hostel address, Monthly rent, One-time security deposit,Lockin Period, Agreement sign time, Landlord address, and Tenant Address.
    2. \n
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    struct RoomAgreement{\n        uint roomid;\n        uint agreementid;\n        string Roomname;\n        string RoomAddresss;\n        uint rent_per_month;\n        uint securityDeposit;\n        uint lockInPeriod;\n        uint timestamp;\n        address payable tenantAddress;\n        address payable landlordAddress;\n    }
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mapping(uint => RoomAgreement) public RoomAgreement_by_No;
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    \n
  1. Now, create a structure for each Rent payment and map that with a uint. This will store details like: Rent No., Hostel no., Agreement No, Hostel name, Hostel address, Monthly rent, Rent payment time, Landlord address, and Tenant Address.
    2. \n
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    struct Rent{\n        uint rentno;\n        uint roomid;\n        uint agreementid;\n        string Roomname;\n        string RoomAddresss;\n        uint rent_per_month;\n        uint timestamp;\n        address payable tenantAddress;\n        address payable landlordAddress;\n    }
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   mapping(uint => Rent) public Rent_by_No;
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    \n
  1. \n

    Create some modifiers that will help you verify a few things before running a function.

    \n

    Here require(...); means that if the given condition is not satisfied, the function won't execute, and the given string will appear as an error code.

    \n
    2. \n
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The following will check if the message sender is the landlord.

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    modifier onlyLandlord(uint _index) {\n        require(msg.sender == Room_by_No[_index].landlord, "Only landlord can access this");\n        _;\n    }
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The following will check if the message sender is anyone except the landlord.

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    modifier notLandLord(uint _index) {\n        require(msg.sender != Room_by_No[_index].landlord, "Only Tenant can access this");\n        _;\n    }
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The following will check whether the room is vacant or not.

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    modifier OnlyWhileVacant(uint _index){\n        \n        require(Room_by_No[_index].vacant == true, "Room is currently Occupied.");\n        _;\n    }
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The following will check whether the tenant has enough Ether in his wallet to pay the rent.

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    modifier enoughRent(uint _index) {\n        require(msg.value >= uint(Room_by_No[_index].rent_per_month), "Not enough Ether in your wallet");\n        _;\n    }
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The following will check whether the tenant has enough Ether in his wallet to pay a one-time security deposit and one month's rent in advance.

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    modifier enoughAgreementfee(uint _index) {\n        require(msg.value >= uint(uint(Room_by_No[_index].rent_per_month) + uint(Room_by_No[_index].securityDeposit)), "Not enough Ether in your wallet");\n        _;\n    }
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The following will check whether the tenant's address is the same as who has signed the previous rental agreement.

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    modifier sameTenant(uint _index) {\n        require(msg.sender == Room_by_No[_index].currentTenant, "No previous agreement found with you & landlord");\n        _;\n    }
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The following will check whether any time is left for the agreement to end.

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    modifier AgreementTimesLeft(uint _index) {\n        uint _AgreementNo = Room_by_No[_index].agreementid;\n        uint time = RoomAgreement_by_No[_AgreementNo].timestamp + RoomAgreement_by_No[_AgreementNo].lockInPeriod;\n        require(now < time, "Agreement already Ended");\n        _;\n    }
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The following will check whether 365 days have passed after the last agreement has been created.

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    modifier AgreementTimesUp(uint _index) {\n        uint _AgreementNo = Room_by_No[_index].agreementid;\n        uint time = RoomAgreement_by_No[_AgreementNo].timestamp + RoomAgreement_by_No[_AgreementNo].lockInPeriod;\n        require(now > time, "Time is left for contract to end");\n        _;\n    }
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The following will check whether 30 days have passed after the last rent payment.

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    modifier RentTimesUp(uint _index) {\n        uint time = Room_by_No[_index].timestamp + 30 days;\n        require(now >= time, "Time left to pay Rent");\n        _;\n    }
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    \n
  1. Now, create some functions
    2. \n
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The following function will be used to add Rooms.

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    function addRoom(string memory _roomname, string memory _roomaddress, uint _rentcost, uint  _securitydeposit) public {\n        require(msg.sender != address(0));\n        no_of_rooms ++;\n        bool _vacancy = true;\n        Room_by_No[no_of_rooms] = Room(no_of_rooms,0,_roomname,_roomaddress, _rentcost,_securitydeposit,0,_vacancy, msg.sender, address(0)); \n        \n    }
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Now, create a function to sign the rental agreement for a hostel room between the landlord and a tenant.

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Before creating the signAgreement function, remember the following:

\n\n

Let's use those modifiers here, so that:

\n\n

Remember those modifiers in point no.10? Use those modifiers here to execute the following function.

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    function signAgreement(uint _index) public payable notLandLord(_index) enoughAgreementfee(_index) OnlyWhileVacant(_index) {\n        require(msg.sender != address(0));\n        address payable _landlord = Room_by_No[_index].landlord;\n        uint totalfee = Room_by_No[_index].rent_per_month + Room_by_No[_index].securityDeposit;\n        _landlord.transfer(totalfee);\n        no_of_agreement++;\n        Room_by_No[_index].currentTenant = msg.sender;\n        Room_by_No[_index].vacant = false;\n        Room_by_No[_index].timestamp = block.timestamp;\n        Room_by_No[_index].agreementid = no_of_agreement;\n        RoomAgreement_by_No[no_of_agreement]=RoomAgreement(_index,no_of_agreement,Room_by_No[_index].roomname,Room_by_No[_index].roomaddress,Room_by_No[_index].rent_per_month,Room_by_No[_index].securityDeposit,365 days,block.timestamp,msg.sender,_landlord);\n        no_of_rent++;\n        Rent_by_No[no_of_rent] = Rent(no_of_rent,_index,no_of_agreement,Room_by_No[_index].roomname,Room_by_No[_index].roomaddress,Room_by_No[_index].rent_per_month,now,msg.sender,_landlord);\n    }
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Now, create a function that the tenant will use to pay the monthly rent to the landlord.

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Before creating the payRent function, remember the following:

\n\n
    function payRent(uint _index) public payable sameTenant(_index) RentTimesUp(_index) enoughRent(_index){\n        require(msg.sender != address(0));\n        address payable _landlord = Room_by_No[_index].landlord;\n        uint _rent = Room_by_No[_index].rent_per_month;\n        _landlord.transfer(_rent);\n        Room_by_No[_index].currentTenant = msg.sender;\n        Room_by_No[_index].vacant = false;\n        no_of_rent++;\n        Rent_by_No[no_of_rent] = Rent(no_of_rent,_index,Room_by_No[_index].agreementid,Room_by_No[_index].roomname,Room_by_No[_index].roomaddress,_rent,now,msg.sender,Room_by_No[_index].landlord);\n    }
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Let's create a function that the landlord will use to mark an agreement complete.

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Before creating agreementCompleted function, remember the following:

\n\n

Let's create a function that the landlord will use to terminate an agreement.

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Before creating agreementTerminated function, remember the following:

\n\n
    function agreementTerminated(uint _index) public onlyLandlord(_index) AgreementTimesLeft(_index){\n        require(msg.sender != address(0));\n        Room_by_No[_index].vacant = true;\n    }
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Compile

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Now, click on the Solidity Compile option in the left sidebar.

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    \n
  1. Select compiler version 0.5.16+
    2. \n
  2. Then click on Compile Hostel.sol
    3. \n
\n

Similar to as follows:

\n\n \n \"Compiler\"\n \n

Deploy

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Click on the Deploy & Run Transactions option in the left sidebar.

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    \n
  1. Choose Environment > JavaScript VM (London)
    2. \n
  2. Now click on Deploy
    3. \n
\n\n \n \"Deploy\"\n \n

🎉 Congratulations, your smart contract has been deployed. 🎉

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Sample Transactions

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Remember that whenever a transaction is getting executed, it stores all the details in a unique hash key.

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Now, under Deployed Contract click on > HOSTEL AT ..... (MEMORY)

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    \n
  1. Click on the V icon (dropdown menu) of addRoom function.
    2. \n
  2. Fill up the details.
    3. \n
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Similar to as follows:

\n\n \n \"AddRoom\"\n \n
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Note: You're entering your details in wei not in ether (1 ether = 1000000000000000000 wei)

\n
\n
    \n
  1. \n

    Then click on transact

    \n

    🎉 Congratulations, you've successfully added your 1st room in the contract. 🎉

    \n

    (You can find the same in the terminal also.)

    \n

    Now the landlord of the room is your 1st Ether Address. (The one with 99.99 test ether in wallet.)

    \n
    2. \n
  2. Change the Account Address from the dropdown menu. (Choose anyone except the one with 99.99 ether)
    3. \n
\n\n \n \"Change\n \n
    \n
  1. Add the total amount you have previously chosen as (rent cost + security deposit)
    2. \n
  2. And then from the dropdown wei, choose ether
    3. \n
\n\n \n \"Change\n \n
    \n
  1. \n

    Scroll down and click on signAgreement, enter 1, and press signAgreement

    \n

    You can check the same by entering RoomAgreementNo : 1

    \n
    2. \n
\n\n \n \"Agreement\n \n

🎉 Congratulations, you've successfully signed your 1st agreement. 🎉

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All your transactions are shown in the terminal.

\n\n \n \"Terminal\"\n \n

Now, you can cross verify this by checking your ether account address.

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Advantages of Smart Contracts

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Now you may ask, \"what's the use of smart contracts when there are several centralized methods?\"

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Let me explain some advantages of smart contracts over centralized systems:

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    \n
  1. Here data cannot be changed or tampered with. So, it is almost impossible for malicious actors to manipulate data.
    2. \n
  2. It's completely decentralized.
    3. \n
  3. Unlike any centralized payment wallet, you don't have to pay any commission percentages to a middle man to transact.
    4. \n
\n

Storage & Others

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You may also ask \"how are all the transactions recorded?\"

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You have to remember that smart contracts store data in a block of the blockchain, and all transactions are stored with a unique hash key.

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In Remix IDE, you can download the complete transactions history as a JSON file. For that, follow these steps:

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    \n
  1. Click Deploy & Run Transaction
    2. \n
  2. Then, expand the Transactions Recorded (..) V dropdown menu.
    3. \n
  3. Then Click on the Save icon.
    4. \n
  4. Press ok.
    5. \n
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Gas Fee

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You may have noticed that whenever a transaction is executed, a few wei is getting deducted from your ether wallet.

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It's called gas fee, which is the payment made by users to compensate for the computing energy required to process and validate transactions.

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As more Ethereum miners come up in near future, the gas fee will decrease in an inverse relation.

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Future Possibilities

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After this, if you want to build a fullstack website using React, you can use this smart contract as a backend.

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For that you need to install/download:

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Frontend:

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    \n
  1. Node.js
    2. \n
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Backend:

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    \n
  1. web3.js
    2. \n
  2. Truffle
    3. \n
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Testing:

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    \n
  1. Ganache
    2. \n
  2. Metamask
    3. \n
\n

Just follow the official documentation of Web3.js to connect your smart contract with your React app.

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Conclusion

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You've successfully understood what Solidity is and how smart contracts work. And you've successfully built and deployed a perfectly working smart contract (where a tenant can pay rent in ether (ETH) directly to the landlord's wallet without paying a single wei to a middle man).

\n

To download the complete code used in this tutorial, click here.

\n

Want to quickly add user login and signup functionality to your React apps? Use LoginRadius for free.

\n","frontmatter":{"date":"November 24, 2021","updated_date":null,"title":"Build Your First Smart Contract with Ethereum & Solidity","tags":["Blockchain","Ethereum","Solidity"],"coverImage":{"childImageSharp":{"fluid":{"aspectRatio":1.5037593984962405,"src":"/static/32b53a158fcbe237c5223007d8b14857/ee604/coverimage.png","srcSet":"/static/32b53a158fcbe237c5223007d8b14857/69585/coverimage.png 200w,\n/static/32b53a158fcbe237c5223007d8b14857/497c6/coverimage.png 400w,\n/static/32b53a158fcbe237c5223007d8b14857/ee604/coverimage.png 800w,\n/static/32b53a158fcbe237c5223007d8b14857/f3583/coverimage.png 1200w","sizes":"(max-width: 800px) 100vw, 800px"}}},"author":{"id":"Aritra Belel","github":"belelaritra","avatar":null}}}},{"node":{"fields":{"slug":"/engineering/blockchain-the-new-technology-of-security-trust/"},"html":"

These days we have all come across one of the coolest buzzwords in the IT industry: \"The Blockchain\". It might seem to be a new magic word in the market that companies spell interest in their businesses. However, the complexity of it is incredibly far-reaching. Blockchain integrates the openness and flexibility of the internet with the security of cryptography to come out with a safer, faster way of verification of information and most importantly establishes trust in this open world.

\n

Blockchain was first developed by an anonymous programmer or group of programmers known by a name 'Santoshi Nakamoto'.It was an underlying technology for the Bitcoin, which is used for peer-to-peer transactions. Blockchain at its heart is a list of transactions like a distributed ledger open to all in the network. It stores the data in such a way that it seems virtually impossible to add, update or remove any information stored without the notice of other users in a peer-to-peer network.

\n

How does blockchain work?

\n

Blockchain mainly performs two tasks: collect and order data in blocks- similar to the traditional computer database and then chain them securely using cryptography.

\n

Let us take a closer look at each block in this enormous chain –

\n\n

\n \n \n

\n

Establishing the trust

\n

The copy of the complete blockchain is with all the participants so that they can detect tampering if the hash matches across the chain then everyone knows that it is trustworthy.\nBlockchain is an emerging technology but has been evolving ever since its innovation. This technology has the unlimited potential to bring about an upheaval in the way everyone- organisations, governments, individuals work together. It promises a simple, secure, paperless path to establish trust for virtual transactions of money, products and other confidential information worldwide.

\n

Blockchain in action

\n

Blockchain is one of the technologies that has gained popularity from its very birth, and now it is being used in many fields.

\n

Financial market

\n

In financial markets, trade is very dynamic where there is the exchange of money, assets involving multiple banks; this may lead to unexpected errors. To reduce this bottleneck blockchain came up with the idea of smart contracts which is a small computer program that describes the transactions step by step combining multiple blockchains, multiple assets and executes the transactions securely.

\n

Digital ID

\n

Blockchain can keep track of many commercial transactions and efficiently hold sensitive information. A digital id via blockchain secures the data stored and can be used worldwide in your fingertips.

\n

Supply chain

\n

Blockchain can be very handy in monitoring the supply chain in food and manufacturing industries by removing paper-based trails and also removing intermediaries between producers to customers. Not just the above applications it is used in many more places and has changed, is going to change the world around us.

\n

Blockchain the next-gen technology

\n

Though it is a new technology, it has an enormous ability to transform everything existing now. As a coin has its two faces, blockchain technology also has some glitches as it can destroy the middlemen in many of the industries.\nBlockchain has already spread its root firmly in soils of the new world, and the swarm of transformation has already begun. It is the responsibility of all the young generation to make complete usage of this technology as it matures and make it to become a huge money plant.

\n","frontmatter":{"date":"October 08, 2020","updated_date":null,"title":"Blockchain: The new technology of trust","tags":["Blockchain","Cyber Security"],"coverImage":{"childImageSharp":{"fluid":{"aspectRatio":1.6666666666666667,"src":"/static/39f6130fcc45e64f3049c5db8f8a19be/14b42/CoverPage.jpg","srcSet":"/static/39f6130fcc45e64f3049c5db8f8a19be/f836f/CoverPage.jpg 200w,\n/static/39f6130fcc45e64f3049c5db8f8a19be/2244e/CoverPage.jpg 400w,\n/static/39f6130fcc45e64f3049c5db8f8a19be/14b42/CoverPage.jpg 800w,\n/static/39f6130fcc45e64f3049c5db8f8a19be/a6352/CoverPage.jpg 960w","sizes":"(max-width: 800px) 100vw, 800px"}}},"author":{"id":"Shraddha V Prasad","github":"shraddhavp","avatar":null}}}}]}},"pageContext":{"tag":"Blockchain"}},"staticQueryHashes":["1171199041","1384082988","2100481360","23180105","528864852"]}