Smart Contracts and Solidity Part-1

Introduction

This article gives an overview on smart contracts, EVM, Basic solidity.

Checkout my previous article on Ethereum vs Ether. And checkout my profile for Ethereum White Paper Simplified series.

Now let's get into this one.

Solidity is an object-oriented, high-level language to implement smart contracts.

Smart contracts

Smart contracts are computer programs which are processed and replicated on all computers in the block chain network.
They allow us to make transactions when certain conditions are met automatically without any coordinator.
These smart contracts on etheruem block chain are written using solidity programming language.

Ethereum Virtual Machine (EVM)

EVM (Ethereum Virtual Machine) is a decentralised computational engine which is present in all the devices participating in ethereum network.
It runs execution and deployment of smart contracts.
Ethereum has 2 types of accounts which are Externally Owned Accounts (EOA) and Contract Accounts. Both of these are treated equally by EVM.
EOAs are controlled by private keys whereas contract accounts are stored in smart contracts, also known as smart wallets.
EVM is a runtime environment used for solidity just like JVM for Java, NodeJS for Javascript.

Solidity Part-1

Initialising a smart contract

In the very first line of every solidity file, we need to specify the compiler version that we are going to use to compile that file.
We do that using pragma solidity <version>
Next thing is to specify the name of the contract. A contract in solidity is equivalent to a class in java.
The syntax to specify a contract is contract <name> { }.

pragma solidity ^0.8.10;

contract Example {
    // code
}

Variables and Datatypes

There are 3 types of variables in solidity. They are :

Local - These are declared inside a function and are not stored on block chain.
State - These are declared outside a function but inside the contract to maintain the state of the smart contract. These are stored on block chain.
Global - These are injected by EVM during the runtime. These provide information about block chain such as timestamps, hash, etc.

A few basic datatypes in solidity are:

uint (unsigned), int(signed) - There are multiple sized uint and int like 8, 16, 32, ..., 256 bits.
bool - For boolean values i.e true or false.
address - A special datatype to store ethereum addresses.
string - To store letters or sentences.
array - To store collection of similar other datatype items.

There are some other datatypes as well which are covered in next articles.

public keyword is used to let those variables or functions accessible from the outside of the contract.
memory keyword is used to make the variables available temporarily rather than entire runtime of contract. It is usually used when passing arguments.

Arrays

Arrays are initialised as <datatype>[] <name>.
push function is used to add item to an array and pop function is used to remove an element from an array.

Loops and Control Structures

Loops are same like in any other programming language. Same while, do-while, for loops.
if, else, break and continue for control statements

Functions

The syntax to write functions is

function <name>(<arguments>) <view/pure> returns (<return type>) { ... }

A view function is a function which doesn't change the state variables of the contract. View functions doesn't require any gas.
We discuss about pure functions in next article.

An example contract using topics discussed above (check comments in program).

pragma solidity ^0.8.10;

contract Example {
    address owner = 0x111122223333444455556666777788889999AAAABBBBCCCCDDDDEEEEFFFFCCCC; // state variable
    function sum (uint num) public view returns (uint) { // A public view function
          uint sum = 0; // local variable
          for(uint i = 0; i <= num; i++) {
              sum = sum + i;
          }
          if(msg.sender == owner) { // msg.sender is global variable
               return sum;
          }
          return 0;
    } // It is a view function because it is not changing the only state variable (owner).
}

Conclusion

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