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https://github.com/pbrudny/learning-solidity-2018

Basic examples of Solidity smart contracts
https://github.com/pbrudny/learning-solidity-2018

blockchain ethereum smart-contracts solidity

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Basic examples of Solidity smart contracts

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README 

        
# learning solidity ~~2018~~ [We are updating this project in 2024 😎]



These examples are part of my guide [The best way to become Ethereum Developer in 2018](https://medium.com/@pbrudny/the-best-way-to-become-ethereum-solidity-developer-in-2018-5606e54646e6)



and `30/30 challenge` on [polish ethereum programming](https://www.facebook.com/groups/531936723867447/?ref=bookmarks) FB group (members write one contract a day to improve Solidity skills).



In Ethereum world everything is changing dynamically.

I decided to make a set of Smart Contracts for learning purposes.



I know it's funny to name a repo this way but I am quite convinced that in 2019 these examples may not work with the latest Solidity.



Try to write a contract yourself before checking the code in the repo!



## Challenges



### 01_say_hello.sol

* set greeting on creation and allow to change it by the owner (creator of the contract)

* return greeting to everyone who calls `sayHello` method

* return `Hello Daddy` to the creator



### 02_balance_address_checker.sol

* return address of the contract

* return address of the contract's owner

* return address of the sender

* return balance of the contract

* return balance of the contract's owner (ONLY if you are the owner)

* return balance of the sender



### 03_basic_random.sol

* return random number 0-99

* the "financial importance" of this calculation is less than miner would get for mining single block

* https://ethereum.stackexchange.com/questions/419/when-can-blockhash-be-safely-used-for-a-random-number-when-would-it-be-unsafe?noredirect=1&lq=1



### 04_lottery_10_users.sol

* 10 users limit

* user has to pay 0.1 ether to join the lottery

* same user can join once

* owner of the contract can join the lottery

* when 10 users join then the winner is picked

* winner receives all the money

* new lottery starts when the winner is pickecd



### 05_lottery_no_limit.sol

* user has to pay 0.1 ether to join the lottery

* no limit for users number   

* same user can join multiple times

* owner of the contract can join too

* owner decides when to pick the winner

* winner receives all the money

* new lottery starts when the winner is pickecd



### 06_lottery_muliple_winners

* no limit for users

* user joins paying 0.1 eth and picking number 1-100

* owner decides when to generate random number (1-100) 

* users who picked generated numbers win

* total prize is distributed to all winners



### 07_fundraising

* fundraising has the goal to reach (amount is set on creation)

* fundraising has the time limit (time is set on creation)

* anyone can add any amount until time is up or the goal is reached

* when the time is up but the goal is not reached users can withdraw their funds

* when the goal is reached owner can withdraw all the money



### 08_basic_token

* intial supply of tokens is set on creation

* contract creator gets initial tokens

* tokens can be transferred to any account

* there is a protection from overflow

* everyone can check balances



### 09_ERC_20_token

* implement ERC20 token based on [the EIP specification]( https://github.com/ethereum/EIPs/blob/master/EIPS/eip-20.md)



### 10_ERC20_usage

* create your own ERC20 token using Open Zeppelin implementation

* inherit from "StandardToken"

* add custom name, symbol, decimals and initial supply



### 11_ERC_721_usage

* create your own ERC721 token using Open Zeppelin implementation

* inherit from "ERC721Token"

* add custom name and symbol



## Other challenges

* [Truffle challenges: 12-29](https://github.com/pbrudny/truffle-challanges)

* [Web3 deploy challenge: 30](https://github.com/pbrudny/web3-deploy-example)



## Contribution

* feel to free to add new challenges in the README.

* feel free to add your solution to any challenge (of course if it's different than the existing one)



### Example: 

If you want to add another Basic Token contract:

1. Fork the repo

2. Add `basic_token_b.sol` to the `07_basic_token` directory

3. Make a PR

4. Let me review it and merge it

5. Enjoy having a nice contribution to the great project :)



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