Data Location

There are three data locations: memory, storage and calldata. These keywords are used to specify the location of the data.

storage is location where state variables are stored. Permanent data on the blockchain.
memory is used to hold temporary values. Lifetime of memory variables limited to an external function call.
calldata is non-modifiable, non-persistent location where function arguments are stored (behaves mostly like memory).

// SPDX-License-Identifier: MIT
pragma solidity ^0.8.24;

contract DataLocations {
    uint256[] public numbers; // 'numbers' is a state variable and is stored in 'storage'

    // 'arr' is a function argument and is stored in 'calldata'
    function addToNumbers(uint256[] calldata arr) public {
        for (uint256 i = 0; i < arr.length; i++) {
            numbers.push(arr[i]); // 'arr[i]' is read from 'calldata'
        }
    }

    // 'x' is a local variable and is stored in 'memory'
    function calculateSum(uint256[] calldata arr) public pure returns (uint256) {
        uint256 sum = 0; // 'sum' is a local variable and is stored in 'memory'
        for (uint256 i = 0; i < arr.length; i++) {
            sum += arr[i]; // 'arr[i]' is read from 'calldata'
        }
        return sum;
    }
}

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