<h1 style="margin-left:0px;">Solidity</h1>Solidity is an object-oriented, high-level language for implementing smart contracts on Ethereum blockchain. Mainly influenced by Javascript, C++ and Python languages.<figure class="image image_resized" style="width:679.985px;"><img src="https://miro.medium.com/v2/resize:fit:588/1*a-06mODkJCRNg5YQXHAa-g.png" alt="" loading="lazy"></figure>Now, we’re going to discuss the features and internals of solidity.Smart contracts are simply programs stored on a blockchain that run when predetermined conditions are met.Popular languages to write smart contracts are Solidity and Vyper for Ethereum or EVM Compatible blockchains and Rust for Solana and a few others.In the following sections, we are going to talk about some of the basics of Solidity.<h1 style="margin-left:0px;">1) SPDX-License-Identifier</h1>To avoid legal issues regards to the copyright, the Solidity compiler encourages the use of machine-readable SPDX-License-Identifier. Every source file should start with a comment indicating its license: // SPDX-License-Identifier: MIT. If you do not want to specify a license or if the source code is not open-source, please use the special value UNLICENSED.<h1 style="margin-left:0px;">2) Pragma and Version Pragma</h1>The ’pragma’ keyword is used to enable certain compiler features or checks. Source files can (and should) be annotated with a version pragma to reject compilation with future compiler versions that might introduce incompatible changes.We can write Solidity versions in header of contract in three ways:<ul><li>pragma solidity 0.8.0 (The source file will only compile exactly on the version 0.8.0 of compiler, else it will throw an error.)</li><li>pragma solidity ^0.8.0 (The source file will only compile on all the versions above 0.8.0 compiler version. Below 0.8.0, the file will not compile and throw error).pragma solidity &gt;=0.8.0 &lt;0.9.0: This means that the source code is to be compiled with a version of Solidity that is greater than or equal to 0.8.0 but less than 0.9.0.</li><li>pragma solidity &gt;=0.8.0 &lt;0.9.0 (This means that the source code is to be compiled with a version of Solidity that is greater than or equal to 0.8.0 but less than 0.9.0.)</li></ul><h1 style="margin-left:0px;">3) Variables in Solidity</h1>There are mainly three types of variables in Solidity:<ol><li>State Variable: Variables whose values permanently stored on contract storage or blockchain.</li><li>Local Variable: Values of these variables are present till the function executes and it cannot be accessed outside that function. This type of variable is usually used to store temporary values.</li><li>Global Variable: Special variables exists in the global namespace used to get information about the blockchain. For eg: block.timestamp, block.difficulty, block.height, etc</li></ol><h1 style="margin-left:0px;">4) Datatypes in Solidity</h1><ol><li>String: Solidity supports String literal using both double quote (“) and single quote (‘). It provides string as a data type to declare a variable of type String.</li></ol><figure class="image image_resized" style="width:487.984px;"><img src="https://miro.medium.com/v2/resize:fit:410/1*2dS1GG6uGmOuGHONZjNW4w.png" alt="" loading="lazy"></figure>2. Array: In Solidity, Array is a data structure, which stores a fixed-size sequential collection of elements of the same type. In Solidity, an array can be of compile-time fixed size or of dynamic size. For storage array, it can have different types of elements as well. In case of memory array, element type cannot be mapping and in case it is to be used as function parameter then element type should be an ABI type. Array can be initialized in solidity as:<figure class="image image_resized" style="width:581.994px;"><img src="https://miro.medium.com/v2/resize:fit:489/1*4qfkTuKaABrsDNDqKfX1-g.png" alt="" loading="lazy"></figure>3. Enum: Enums restrict a variable to have one of only a few predefined values. The values in this enumerated list are called enums.<figure class="image image_resized" style="width:311.998px;"><img src="https://miro.medium.com/v2/resize:fit:262/1*P-OuntmZhHKnjDb1jkGEvQ.png" alt="" loading="lazy"></figure>4. Struct: Struct types are used to represent a record. It defined by initializing more than one simple datatypes in it. We can say, struct is a complex datatype just like strings, uint, array, etc. To define a Struct, you must use the struct keyword. The struct keyword defines a new data type, with more than one member. The format of the struct statement is as follows:<figure class="image image_resized" style="width:421.987px;"><img src="https://miro.medium.com/v2/resize:fit:354/1*HTsXifeTbVEcag_2E8Ud1A.png" alt="" loading="lazy"></figure>5. Ether Units: In solidity, to deploy the smart contract on blockchain, we need to pay gas fee. The gas fee mainly paid in form of ‘Ethers’ on Ethereum blockchain. Different blockchains have various tokens to pay gas fee. Gas fee and Ether can understood with analogy of “Money” and “Rupee”. The smallest unit is ‘Wei’ and the biggest unit is ‘Ether’.<figure class="image image_resized" style="width:679.985px;"><img src="https://miro.medium.com/v2/resize:fit:588/1*hQZw8irtzeNE8x4BMPkxKQ.png" alt="" loading="lazy"></figure>6. Special Variables: Special variables are globally available variables and provides information about the blockchain. Following is the list of special variables -<figure class="image image_resized" style="width:679.985px;"><img src="https://miro.medium.com/v2/resize:fit:588/1*jfb3fn8oBlOumutD3M-Nzw.png" alt="" loading="lazy"></figure>7. Events : Event is an inheritable member of a contract. An event is emitted, it stores the arguments passed in transaction logs. These logs are stored on blockchain and are accessible using address of the contract till the contract is present on the blockchain. An event generated is not accessible from within contracts, not even the one which have created and emitted them.<figure class="image image_resized" style="width:582.998px;"><img src="https://miro.medium.com/v2/resize:fit:490/1*kcbyywbNOhoIr8aVXxYlXA.png" alt="" loading="lazy"></figure><h1 style="margin-left:0px;">5) Functions in Solidity</h1><ol><li>Function: The most common way to define a function in Solidity is by using the function keyword, followed by a unique function name, a list of parameters (that might be empty), and a statement block surrounded by curly braces. The basic syntax is shown here.</li></ol><figure class="image image_resized" style="width:581.994px;"><img src="https://miro.medium.com/v2/resize:fit:489/1*Q-4axTEcjcEdFvgL5i7Kog.png" alt="" loading="lazy"></figure>2. Modifiers: Function Modifiers are used to modify the behaviour of a function. We can say to add prerequisites to a function. For example- What conditions, a particular function has to obey before execution.<figure class="image image_resized" style="width:581.994px;"><img src="https://miro.medium.com/v2/resize:fit:489/1*JSSh4-9FwLiB54BrhNx6rg.png" alt="" loading="lazy"></figure>3. View function: View functions ensure that they will not modify the state. A function can be declared as view. We can just view the variables but cannot modify the state of contract. For Ex- Getter method are by default view functions.<figure class="image image_resized" style="width:587.984px;"><img src="https://miro.medium.com/v2/resize:fit:494/1*J6_IZ5K0ZBbx803hMFijIw.png" alt="" loading="lazy"></figure>4. Pure function: Pure functions ensure that they not read or modify the state. A function can be declared as pure. Pure functions can use the revert() and require() functions to revert potential state changes if an error occurs. We can say these functions are not dependent on the contract variables.<figure class="image image_resized" style="width:581.994px;"><img src="https://miro.medium.com/v2/resize:fit:489/1*7930crc2YQsk4O627DocMA.png" alt="" loading="lazy"></figure>5. Payable function: The presence of payable keyword in the function means that the function can take transaction in ethers and the balance will be stored in contract balance. If a transaction that transfers Ether comes to the contract and calls some function X, then if this function X does not have the payable modifier, then the transaction will be rejected.<figure class="image image_resized" style="width:582.998px;"><img src="https://miro.medium.com/v2/resize:fit:490/1*8OTCPS_waV9BgILZNPV4Hg.png" alt="" loading="lazy"></figure>6. Fallback function: Fallback is the special type of function which is called when a non-existent function is called. Fallback function has no name as well as it doesn’t take any argument. It main purpose is to take ‘Calldata’ value from the user but we can make it to take ‘Ethers’ by making it ‘payable’ and ‘external’.<figure class="image image_resized" style="width:585.993px;"><img src="https://miro.medium.com/v2/resize:fit:492/1*XJ2nhWk4OSSzCbAlQ-BvPw.png" alt="" loading="lazy"></figure>7. Receive function: <code>receive</code> is a new keyword in Solidity 0.6.x that is used as a fallback function that is only able to receive ether.<ul><li><code>receive() external payable</code> — for empty Calldata (and any value).</li></ul>The <code>receive</code> method is used as a fallback function in a contract and is called when ether is sent to contract with no calldata. If the <code>receive</code> method does not exist, it will use the <code>fallback</code> function.<figure class="image image_resized" style="width:582.998px;"><img src="https://miro.medium.com/v2/resize:fit:490/1*pdwtRozCeGa-kweOficiBg.png" alt="" loading="lazy"></figure>8. Constructor: Constructor is a special function declared using constructor keyword. It is an optional function and is used to initialize state variables of a contract. A contract have only one constructor. In case, base contract have constructor with arguments, each derived contract have to pass them.<figure class="image image_resized" style="width:439.993px;"><img src="https://miro.medium.com/v2/resize:fit:370/1*obPkRcauPsHmFDG47KwvdA.png" alt="" loading="lazy"></figure>Conclusion: As a conclusion, Solidity programming language is a flexible and easy-to-understand language. It helps in developing smart contracts. It is also the preferred language for Blockchain development, focused on Ethereum.Note For Beginners in programming: For beginners, I just suggest not to start with solidity as a first language to learn programming. First, give some time to C/C++ or JAVA or Javascript and then you are good to go (By the way, I personally started with Javascript and frontend development and then solidity. But I prefer you to start with a little bit of C++ or Java as they are core of programming and then you can go with Javascript or Python. You can also do blockchain, if you’re only familiar with python).Note For Beginners in Blockchain: If you already have hands on programming, you’re good to go with that revise all your Javascript concepts and specifically AJAX and then start with solidity.We will be doing one more article on this in the coming week as an “Advanced” version.If you appreciate what we are doing, please follow us on <a href="https://twitter.com/_BuildBear">Twitter</a> and <a href="https://t.me/+6mjOnBFUR9xjN2U1">Join the Telegram</a> group if you haven’t done yet.Author:Vivek Tyagi is always open to feedback and learning.<a href="www.linkedin.com/in vivek-tyagi- a7a210165">LinkedIn</a> - <a href="twitter.com/whyviccky">Twitter</a>

Getting to know Solidity || Solidity 101

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