root💀senseicat:~#

Hack. Eat. Sleep. Repeat!!!

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Solidity Basics

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• Installing solcjs

sudo npm install --global solc

• Specifying the version

//version
pragma solidity 0.8.30; //use only 0.8.30
//use versions between 0.8.19 and 0.9.0 (excluded)
pragma solidity ^0.8.19;
pragma solidity >=0.8.19 <0.9.0;

• SPDX License Identifier, use

  //SPDX-License-Identifier: MIT
  //solidity version
  pragma solidity ^0.8.30;
  

• Running with solcjs-:

solcjs --bin main.sol

• Code-:

//SPDX-License-Identifier: MIT
//solidity version
pragma solidity ^0.8.30;

contract simpleStorage {
    //code goes thus
}

• Bool-:

bool hasFavoriteNumber = true; //true or false

• Basic types-:

   bool hasFavoriteNumber = true;
    uint256 favoriteNumber = 88;
    string favoriteNumberInText = "eighty-eight";
    int256 favoriteInt = -88;
    address myAddress = 0xAB1b7206aa6840C795aB7A6AE8b15417B7E63A8D;
    bytes32 favoriteBytes32 = "cat";

• create a function with function-:

//SPDX-License-Identifier: MIT
pragma solidity ^0.8.1;

contract Storage{
    uint256 digit = 100;
    function store(uint256 _digit) public {
        digit = _digit;
    }
}

• Appending the public keyword next to a variable will automatically change its visibility and it will generate a getter function (a function that gets the variable’s value when called).

uint256 public digit = 1000;

• Visibility for variables and function-:

public
private
internal
external

• Pure and view functions-:

//SPDX-License-Identifier: MIT
pragma solidity ^0.8.1;

contract Storage{
    uint256 digit = 100;
    function store(uint256 _digit) public {
        digit = _digit;
    }
    //view
    function retrieve() public view returns {
        return digit;
    }
    //pure
    function retrieve() public pure returns {
        return 7;
    }
}

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Arrays and Structs

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• Creating a list of uint256 numbers-:

uint256[] digits = [0,10,90];

• The issue with this data structure above is that we cannot link the owner with its favorite value. One solution is to establish a new type using the struct keyword, named Person, which is made of two attributes: a favorite number and a name.

struct Person {
   string name;
   uint256 age;
}

• Using it-:

Person public ade = Person("Ade",100);

• Array of struct-: Creating individual variables that represent several people might become a tedious task, due to the repetitive steps of the process. Instead of manually instantiating a variable for each person, we can combine the two concepts we just learned about: arrays and structs.

Person[] public people;
Person[3] public three_people;

• Pushing new values to an array of structs with a function.

//function push to three_people array
    function push_value(uint256 _negativeNumber, string memory _name) public{
        people.push(Person(_negativeNumber,_name));
  }

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Memory Storage

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• How does solidity handle data storage? It uses locations like this-:

Calldata
Memory
Storage
Stack
Code
Logs

• Calldata and memory are temporary storage locations during function execution.calldata is read-only, used for function inputs that can’t be modified. In contrast, memory allows for read-write access, letting variables be changed within the function. To modify calldata variables, they must first be loaded into memory.
• Memory-:

string memory name = "Ade";

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