Cryptozombie Part 1

This is a summary of learning solidity by building a Dapp game

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Learning summary:

■  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.

■ State variables are permanently stored in contract storage. This means they're written to the Ethereum blockchain. Think of them like writing to a DB.

The uint data type is an unsigned integer, meaning its value must be non-negative. There's also an int data type for signed integers.

■ Structs allow you to create more complicated data types that have multiple properties.

■ There are two types of arrays in Solidity: fixed arrays and dynamic arrays:

e.g uint[2] fixedArray;

      string[5] stringArray;

      uint[ ] dynamicArray; // a dynamic Array - has no        fixed size, can keep growing

      array.push() adds something to the end of the          array

■ A function declaration in solidity looks like the following:

  function eatHamburgers(string _name, uint _amount) {

}

■ In Solidity, functions are public by default. This means anyone (or any other contract) can call your contract's function and execute its code. However it's a good practice to mark your functions as private by default, and then only make public the functions you want to expose to the world.

■ Return Values

To return a value from a function, the declaration looks like this:

■ Ethereum has the hash function keccak256 built in, which is a version of SHA3. A hash function basically maps an input string into a random 256-bit hexidecimal number. A slight change in the string will cause a large change in the hash.

■ Events are a way for your contract to communicate that something happened on the blockchain to your app front-end, which can be 'listening' for certain events and take action when they happen.

once Solidity contract is completed, we need to write a javascript frontend that interacts with the contract. Ethereum has a Javascript library called Web3.js. In the later article, I'll go over in depth how to deploy a contract and set up Web3.js.