Month: April 2021

This is a barebones walkthrough for developing a blockchain decentralized app (Dapp) for Etherium (ERC-20) based tokens. Goal is to go through all the steps needed to set up initial environment and build a first contract that compiles, deploys, test, and can interact with via web3.js Javascript in a web browser.

Step 4: Truffle Develop Console

In this step we will look at the Truffle console before starting testing. Be sure to complete Steps 1 to Step 3 before attempting this step.

1. At the command line in the project folder type:

truffle develop

This will start a development blockchain server and generate 10 test wallets. (NOTE: this is not real Etherium and will not work on MAINNET)

2. You are now in the Truffle development console. You can use the generated public and private wallet keys to test your DApp transactions.

3. You can also compile your project in the console with the command “compile”

truffle(develop)> compile

4. You can deploy your project in the console with the command “deploy”

truffle(develop)> deploy

In the next step we will create a test package and run the test from the console.

Continue to Step 5 – Coming Soon!

Error Message:

The Windows Server Failover Clustering (WSFC) resource control API returned error code 5057. The WSFC service may not be running or may not be accessible in its current state, or the specified arguments are invalid. For information about this error code, see “System Error Codes” in the Windows Development documentation.

At command prompt enter:

NET HELPMSG for 5057

You will then see that 5057 means “The cluster IP address is already in use.”

You can then ping – a the IP addresses and see which ones are in use.

This is a barebones walkthrough for developing a blockchain decentralized app (Dapp) for Etherium (ERC-20) based tokens. Goal is to go through all the steps needed to set up initial environment and build a first contract that compiles, deploys, test, and can interact with via web3.js Javascript in a web browser.

Step 3: Creating Variables and Functions

In this step we will add comments, state variables and functions to our contract. Be sure to complete Step 1 and Step 2 before attempting this step.

1. Comments can be designated in two ways. Use the // for single line and /* */ for multiline comments

// this is a single line comment
/*
   use this for
   multiline comments
*/

2. State variables are variables whose values are permanently stored in the blockchain. You can declare a state variable in the body of the contract. Visibility can be public, internal or private for state variables. A public state variable gets an automatically generated “getter” function.

Each statement ends with a semi-colon “;”

Also we will be using the datatype “uint” (not to be confused with ‘unit’) which stands for unsigned integer.

Add the following to the body of your contract.

//contract state variable
uint myVariable = 0;

3. Functions are the bits of code that do something.

If the function reads but does not make any changes to the state of the contract it can be declared as a “view” function. If the function only acts on the input and does not read the state of the contract it can be declared as a “pure” function. These designations are important as they can help reduce the cost of Etherium to process the contract.

Visibility can be external, public, internal or private for functions.

Also, a common convention is to add an underscore to function parameters to avoid confusion between state variables at the contract scope and parameters in the function scope.

Add the following two functions to the body of your contract below the constructor.

function setMyVariable(uint _x) public {
   myVariable = _x;
}

function getMyVariable () public view returns (uint) {
   return myVariable;
}

10. Now save the file (in most editors is shortcut keys “Ctrl + s”). Now return to the Command Prompt window and compile your contract.

truffle compile

You should get results like the following. If you get any errors be sure the file is located in the right folder, the code matches, and the file has been saved.

Continue to Step 4 – Truffle Develop Console

This is a barebones walkthrough for developing a blockchain decentralized app (Dapp) for Etherium (ERC-20) based tokens. Goal is to go through all the steps needed to set up initial environment and build a first contract that compiles, deploys, test, and can interact with via web3.js Javascript in a web browser.

Step 2: Creating a Contract

In this step we will set up the project, then create and compile an empty contract. Be sure to complete Step 1 before attempting this step.

1. Open a Command Prompt terminal. Can search for “cmd” in the start menu.

2. Create a folder to house your project. For this example create a projects folder and myfirstdapp subfolder.

c:
cd c:\
mkdir projects
cd projects
mkdir myfirstdapp
cd myfirstdapp

3. Create the folder structure for the Truffle project with the command:

truffle init

4. The project files can be created and edited with any text editor. It is helpful to use a tool that helps navigate the project. In this example we are using Atom. If you have Atom installed, you can just type “atom .” at the command prompt. Otherwise open your editor and navigate to the project folder.

atom .

5. We will be working mostly with the “contracts” and “test” folders for now.

contracts/: Directory for Solidity contracts
migrations/: Directory for scriptable deployment files
test/: Directory for test files for testing your application and contracts
truffle-config.js: Truffle configuration file

6. Navigate to the contracts folder and create a file named “MyContract.sol”

7. The very first line of every contract file will be the pragma indicating what version of solidity the contract was coded for. If you are following this tutorial using a newer version, then may need to update this value. More info on the structure of contracts is available here.

pragma solidity ^0.5.0;

8. Next will be the declaration of the contract. Note that the name of the contract and the file should match.

contract MyContract {
}

9. Next will be the construction declaration for the contract which goes inside the contract declaration. Note that the constructor is declared as public.

   constructor() public{
   }

10. Now save the file (in most editors is shortcut keys “Ctrl + s”). You now have the minimum code for a contract. To compile the contract return to the Command Prompt window and type:

truffle compile

You should get results like the following. If you get any errors be sure the file is located in the right folder, the code matches, and the file has been saved.

Continue to Step 3 – Variables and Functions