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LEARN SOLIDITY LESSON 4: Keccak256. Typecasting. Events Solidity

LEARN SOLIDITY LESSON

Keccak256 Solidity. Typecasting Solidity. Events Solidity


Keccak256 Solidity

Ethereum has the hash function keccak256 built in, which is a version of SHA3. A hash function basically maps an input into a random 256-bit hexadecimal number. A slight change in the input will cause a large change in the hash.
//6e91ec6b618bb462a4a6ee5aa2cb0e9cf30f7a052bb467b0ba58b8748c00d2e5
keccak256(abi.encodePacked("aaaab"));
//b1f078126895a1424524de5321b339ab00408010b7cf0e6ed451514981e58aa9
keccak256(abi.encodePacked("aaaac"));

Typecasting Solidity

Sometimes you need to convert between data types. Take the following example:

int8 a = 5;
uint b = 6;
uint8 c = a * uint8(b);

Events Solidity

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.
//SOLIDITYevent IntegersAdded(uint x, uint y, uint result);

function add(uint _x, uint _y) public returns (uint) {
  uint result = _x + _y;
  // run
  emit IntegersAdded(_x, _y, result);
  return result;
}//JAVASCRIPTYourContract.IntegersAdded(function(error, result) {
  // do something with result
})


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