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+# ethereum
+[app example](https://github.com/StephenGrider/EthereumCasts)
+
+
+# smart contracts
+[Linux Foundation Hyperledger Fabric](https://www.hyperledger.org/projects/fabric)
+[hyperledger composer playground](http://composer-playground.mybluemix.net/login)
+[hyperledger composer playground tutorial](https://hyperledger.github.io/composer/latest/tutorials/playground-tutorial.html)
+```
+# application schema
+Business Application -> Hyperledger Composer -> Blockchain ( Hyperledger Fabric)
+```
+[documentation](http://solidity.readthedocs.io/en/latest/)
+
+---
+user app to communicate with Ethereum
+* Metamask ( chrome extension )
+* Mist browser
+
+---
+[Rinkeby ethereum account charger](rinkeby-faucet.com)
+[Rinkeby ethereum charger](https://faucet.rinkeby.io/)
+
+---
+
+## account address types:
+* external ( user account, common for all networks )
+* internal ( contract account, specific for each network )
+```
+balance
+storage - data storage
+code - compiled machine code 
+```
+
+## account credential saving
+[bip39](https://iancoleman.io/bip39/)
+
+## [smart contract playground](http://remix.ethereum.org)
+
+
+## SmartContract API collaboration via nodejs app example
+* NodeJS ( min version 8.0.1 )
+```
+# ganache-cli 
+const Web3 = require('web3')
+const web3 = new Web3("http://localhost:8545")
+
+console.log(web3.eth.getAccounts().then(e=>console.log(e)))
+```
+* [Java](https://docs.web3j.io/getting_started.html)
+* [SpringBoot, gradle example, maven plugin](https://github.com/web3j/)
+
+http://solidity.readthedocs.io/en/latest/
+
+## contract development phases:
+* create project
+```
+npm init
+npm install -save solc
+
+```
+* contract creation ( solidity compiler )
+* local testing ( Mocha framework )
+```
+# npm install mocha ganache-cli web3@1.0.0-beta.26
+npm install mocha ganache-cli web3
+ 
+```
+* deployment ( script )
+```
+truffle
+```
+
+# [syntax](http://solidity.readthedocs.io/en/latest/)
+[code examples](https://solidity.readthedocs.io/en/latest/solidity-by-example.html)
+[references](https://solidity.readthedocs.io/en/latest/solidity-in-depth.html)
+[source code of the smart contracts](https://github.com/ethereum/solidity)
+
+## syntax highlighters
+* [Atom](https://atom.io/packages/language-ethereum)
+```
+Open the package installation manager in atom and search for 'language-ethereum'. After installing the package, you might have to manually change the highlighter in the .sol file. Look for the selector at the bottom right of your editor window.
+```
+[Sublime](https://packagecontrol.io/packages/Ethereum)
+[VSCode](https://github.com/juanfranblanco/vscode-solidity)
+[Webstorm](https://plugins.jetbrains.com/plugin/9475-intellij-solidity)
+[VIM](https://github.com/tomlion/vim-solidity)
+
+## array types
+* fixed array
+```
+uint[5] exampleOfFixedArray;
+```
+* dynamic array
+```
+string[] public exampleOfDynamicPublicArray;
+```
+
+## function types
+* public/private ( default - public )
+* view/constant ( return field, return constant)
+* pure ( don't use any contract-variables to manipulate, 'pure' functions  )
+* payable 
+
+
+## useful functions
+* eccak256 
+```
+built in, which is a version of SHA3. A hash function basically maps an input string into a random 256-bit hexidecimal number.
+example:
+//b1f078126895a1424524de5321b339ab00408010b7cf0e6ed451514981e58aa9
+keccak256("aaaac");
+```