Skip to main content

​
Overview

The SimpleStorage contract is a foundational smart contract that demonstrates core Solidity concepts. It manages a favorite number and maintains a list of people with their associated favorite numbers. Key Features:
  • Store and retrieve a favorite number
  • Manage a dynamic list of people with their favorite numbers
  • Quick name-to-number lookup using mappings
  • Demonstrates structs, arrays, and mappings in action

​
Contract Structure

​
State Variables

uint256 myFavoriteNumber = 3;
Person[] public listOfPeople;
mapping(string => uint256) public nameToNumber;
  • myFavoriteNumber - Stores a single unsigned integer (initialized to 3)
  • listOfPeople - Dynamic array of Person structs
  • nameToNumber - Maps person names to their favorite numbers for efficient lookup

​
Data Types

​
Person Struct

struct Person {
    uint256 favoriteNumber;
    string name;
}
The Person struct defines a custom data type that bundles together a person’s name and their favorite number.

​
Core Functions

​
store()

function store(uint256 _favoriteNumber) public {
    myFavoriteNumber = _favoriteNumber;
}
Stores a new favorite number, overwriting the previous value. Parameters:
  • _favoriteNumber - The new favorite number to store
Visibility: public - Can be called by anyone
This is a state-changing function that costs gas to execute since it modifies blockchain storage.

​
retrieve()

function retrieve() public view returns (uint256) {
    return myFavoriteNumber;
}
Retrieves the currently stored favorite number. Returns: The current value of myFavoriteNumber Visibility: public view - Read-only function that doesn’t cost gas when called externally

​
addPerson()

function addPerson(string memory _name, uint256 _favoriteNumber) public {
    listOfPeople.push(Person(_favoriteNumber, _name));
    nameToNumber[_name] = _favoriteNumber;
}
Adds a new person to the list and creates a mapping entry for quick lookup. Parameters:
  • _name - The person’s name (stored in memory during function execution)
  • _favoriteNumber - The person’s favorite number
What it does:
  1. Creates a new Person struct
  2. Adds it to the listOfPeople array
  3. Creates a mapping entry for name-based lookup
The memory keyword indicates that _name is temporarily stored in memory during function execution, not permanently in contract storage.

​
Full Contract Code

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

contract SimpleStorage {
    uint256 myFavoriteNumber = 3;

    struct Person {
        uint256 favoriteNumber;
        string name;
    }

    Person[] public listOfPeople;
    mapping(string => uint256) public nameToNumber;

    function store(uint256 _favoriteNumber) public {
        myFavoriteNumber = _favoriteNumber;
    }

    function retrieve() public view returns (uint256) {
        return myFavoriteNumber;
    }

    function addPerson(string memory _name, uint256 _favoriteNumber) public {
        listOfPeople.push(Person(_favoriteNumber, _name));
        nameToNumber[_name] = _favoriteNumber;
    }
}

​
Usage Examples

// Store the number 42
simpleStorage.store(42);

​
Concepts Demonstrated

Data Types

  • uint256 for numbers
  • string for text
  • Custom struct types

Storage Structures

  • Dynamic arrays (Person[])
  • Mappings for key-value pairs
  • State variables

Functions

  • State-changing functions
  • view functions for reading
  • Public visibility

Memory Keywords

  • memory for temporary data
  • Understanding storage locations

​
Key Takeaways

SimpleStorage teaches fundamental Solidity concepts:
  • How to declare and use state variables
  • Working with structs, arrays, and mappings
  • The difference between view and state-changing functions
  • Memory vs storage data locations
  • Public visibility and automatic getters
In production contracts, consider adding access controls to prevent unauthorized modifications to stored data.

Build docs developers (and LLMs) love

Get started for freeTalk to us