Solidity Blockchain - Memory,Storage and mapping explanation brief explanation [closed] - cryptography

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Kindly someone can explain me about mapping,storage and memory breifly with examples ? I am not clear with some articles
Thanks!!

Answer 1

STORAGE AND MEMORY
Storage and Memory keywords in Solidity are analogous to Computer’s hard drive and Computer’s RAM. Much like RAM, Memory in Solidity is a temporary place to store data whereas Storage holds data between function calls. The Solidity Smart Contract can use any amount of memory during the execution but once the execution stops, the Memory is completely wiped off for the next execution.
Whereas Storage on the other hand is persistent, each execution of the Smart contract has access to the data previously stored on the storage area.
Every transaction on Ethereum Virtual Machine costs us some amount of Gas. The lower the Gas consumption the better is your Solidity code. The Gas consumption of Memory is not very significant as compared to the gas consumption of Storage. Therefore, it is always better to use Memory for intermediate calculations and store the final result in Storage.
State variables and Local Variables of structs, array are always
stored in storage by default.
Function arguments are in memory.
Whenever a new instance of an array is created using the keyword
‘memory’, a new copy of that variable is created.
Changing the array value of the new instance does not affect the
original array.
Example#1: In the below example, a contract is created to demonstrate the ‘storage’ keyword.
pragma solidity ^0.4.17;
// Creating a contract
contract helloGeeks
{
// Initialising array numbers
int[] public numbers;
// Function to insert values
// in the array numbers
function Numbers() public
{
numbers.push(1);
numbers.push(2);
//Creating a new instance
int[] storage myArray = numbers;
// Adding value to the
// first index of the new Instance
myArray[0] = 0;
}
}
Output:
When we retrieve the value of the array numbers in the above code, Note that the output of the array is [0,2] and not [1,2].
Example#2: In the below example, a contract is created to demonstrate the keyword ‘memory’.
pragma solidity ^0.4.17;
// Creating a contract
contract helloGeeks
{
// Initialising array numbers
int[] public numbers;
// Function to insert
// values in the array
// numbers
function Numbers() public
{
numbers.push(1);
numbers.push(2);
//creating a new instance
int[] memory myArray = numbers;
// Adding value to the first
// index of the array myArray
myArray[0] = 0;
}
}
Output:
When we retrieve the value of the array numbers in the above code, Note that the output of the array is [1,2]. In this case, changing the value of myArray does not affect the value in the array numbers, this because the function stopped, the the array wasn't saved
MAPPINGS
Mappings are a totally different thing.
These are used to store the data in the form of key-value pairs, a key can be any of the built-in data types but reference types are not allowed while the value can be of any type.
Mappings are mostly (but not limited to) used to associate the unique Ethereum address with the associated value type.
The mappings are quite similar to an array
mapping(key => value) <name>;
Example#1:
pragma solidity ^0.4.17;
// Creating a contract
contract helloGeeks
{
// Initialising mapping of user balance
mapping(address => uint) balance;
// Function to insert user balance
function Insert(address _user, uint _amount) public
{
//insert the amount to a specific user
balance[_user] = _amount
}
//function to view the balance
function View(address _user) public view returns(uint)
{
//see the value inside the mapping, it will return the balance of _user
return balance[_user];
}
}