The pure, view, and payable functions

Functions can be declared as pure, view, or payable, depending on whether it can receive Ether or whether it needs to access the state. Some earlier versions of Solidity had a constant as the alias to view, but it was dropped in version 0.5.0:

• Pure function: A pure function means it won’t read or modify the state
• View function: A view function means it won’t alter the storage state in any way, but you can view it
• Payable function: A payable function means it can receive Ether

Here is an example of the pure, view, and payable functions:

 //pure
  function add(uint a, uint b) public pure returns(uint) {   }
//view
  function add(uint a, uint b) public view returns(uint) {   }
// payable
function send() payable { }

The state means anything EVM holds beyond the input parameters, including state variables, events, contracts, Ether, and more. The following are...