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Developing Etherium Dapp on your Windows PC using Truffle – Step 3

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 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;
State variable declaration

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.

Compile, Compile …

Continue to Step 4 – Coming Soon!

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Developing Etherium Dapp on your Windows PC using Truffle – Step 2

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.

Open a cmd prompt window

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
Create folder for project

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

truffle init
Initialize Truffle project

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 .
Project folder open in 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”

Your first contract

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;
First line is version pragma

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

contract MyContract {
}
Contract declaration

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{
   }
An empty contract

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.

Your first compile… of many…

Continue to Step 3 – Variables and Functions

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Developing Etherium Dapp on your Windows PC using Truffle – Step 1

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 1: Pre-Requisites

In this step we download and install the needed tools to set up our development environment.

Git is needed to retrieve software packages. Download and install Git for Windows: https://git-scm.com/download/win

Node.js is a server that allows execution of Javascript outside of a browser. Also includes NPM for downloading modules and packages. Download and install Node.js: https://nodejs.org/

Ganache gives you your own local blockchain node to develop with. Download and install Ganache: https://www.trufflesuite.com/ganache

MetaMask is crypto wallet & gateway to blockchain apps that turns your browser into a blockchain browser. You will also need to use a compatible browser such as Brave, Chrome, Firefox, or Edge. Install MetaMask: https://metamask.io/download.html

Install Truffle. After you have installed Nodejs, Truffle can be installed using NPM. Open up cmd shell and enter:

npm install -g truffle

It is also helpful to use a text editor that recognizes the Etherium programming language Solidity, for example:

For this walkthrough we will be using Atom.

Continue to Step 2 – Creating a Contract