Manipulating strings in Solidity is notoriously difficult. This is surprising for most developers who are used to manipulating easily in other programming languages like Javascript or Python. https://youtu.be/gNlwpr3vGYM In this article I give a couple of useful code snippets to do some simple string manipulations in Solidity. Warning: Keep in…

Generating a random number in a smart contract is very useful, especially for games. Can we do this in Solidity? Yes! https://youtu.be/4zvvZf-byok Here is the code: pragma solidity ^0.6.0; contract MyContract { function _randModulus(uint mod) internal returns(uint) { return uint(keccak256(abi.encodePacked( now, block.difficulty, msg.sender) )) % mod; nonce++; return rand; }…

ERC this, ERC that... so many token standards... If you want to become good in Solidity, you HAVE to understand how to transfer on-chain assets... And that means knowing token standards, like ERC20... The problem is... there are SO MANY token standards: What is an Ethereum Token? Which tokens are…

Let's say we have 2 smart contracts. A and B. A calls B, and B throws an error. What happen in A? Not sure? haha, that's a tricky one! Actually it depends on how B was called. If B was called the normal way, the whole transaction get reverted: contract A {…

https://youtu.be/-5j6Ho0Bkfk ERC20 tokens allow you to create your own coin inside Ethereum.  They are used in many projects to represent financial assets, in-game assets, collectible, and other kind of assets. At some point in your project, you will probably need to interact with them. And most often, you will need to…

https://youtu.be/_Nvl-gz-tRs Sending Ether between smart contracts is very important. After all, it's because smart contracts can do financial transactions that they are so powerful. But surprisingly there are a few caveats when you want to send ether from a smart contract: Transfer units are in wei (10^-18 ether), not ether…

https://youtu.be/MPBOnChpi0c Solidity arrays... are like Javascript arrays, right? Nope.. In Solidity: Arrays can only contain data of the same type (ex: arrays of integers, array of booleans, but not arrays of integers AND booleans..) Arrays can be in storage, or in memory (persistent and non-persistent) You can use the `push()`…

Finally! Smart contract 30 is finished! I have just published the last video of smart contract 30 on Solidity assembly. In total this course has 56 videos and is 13.6 hours long. It took me almost 6 month of efforts to do all the research, coding and recording. I gave…

Simple transactions on Ethereum cost from 20-30 cents to a few dollars. But complex transactions can be much more expensive. For example, the Loom network created the ERC721x standard to avoid paying millions of dollars in gas costs when doing a batch token transfer. Clearly, knowing how to reduce gas…

After you deploy a web application, you can always change its code if you need to add a feature or fix a bug. All you need to do is to redeploy the code on the server. With Ethereum smart contracts, this is not possible. Once you deploy a smart contract,…