Index

Chapter 2 Contracts

Chapter 2: Contracts

Starting with the absolute basics:
Solidity's code is encapsulated in contracts. A contract is the fundamental building block of Ethereum applications — all variables and functions belong to a contract, and this will be the starting point of all your projects.
An empty contract named HelloWorld would look like this:

contract HelloWorld {

}

Version Pragma

All solidity source code should start with a "version pragma" — a declaration of the version of the Solidity compiler this code should use. This is to prevent issues with future compiler versions potentially introducing changes that would break your code.
It looks like this: pragma solidity ^0.4.25; (for the latest solidity version at the time of this writing, 0.4.25).
Putting it together, here is a bare-bones starting contract — the first thing you'll write every time you start a new project:

pragma solidity ^0.4.25;

contract HelloWorld {

}

Put it to the test

To start creating our Zombie army, let's create a base contract called ZombieFactory.
1. In the box to the right, make it so our contract uses solidity version 0.4.25.

2. Create an empty contract called ZombieFactory.

When you're finished, click "check answer" below. If you get stuck, you can click "hint".

pragma solidity ^0.4.25;

contract ZombieFactory {

//start here

}