Interface

function totalSupply() public constant returns (uint);

function balanceOf(address tokenOwner) public constant returns (uint balance);

function allowance(address tokenOwner, address spender) public constant returns (uint remaining);

function transfer(address to, uint tokens) public returns (bool success);

function approve(address spender, uint tokens) public returns (bool success);

function transferFrom(address from, address to, uint tokens) public returns (bool success);

event Transfer(address indexed from, address indexed to, uint tokens);

event Approval(address indexed tokenOwner, address indexed spender, uint tokens);

Explanation of each method:

• https://en.bitcoinwiki.org/wiki/ERC20
• https://github.com/OpenZeppelin/openzeppelin-contracts/blob/master/contracts/token/ERC20/IERC20.sol

Code Notes

• You cannot get "existing" keys for a mapping. You'd have to store them separately.
• public contract variables automatically have a getter created for them, but not a setter.
• When a require condition is not met, all prior transactions are undone.
• Useful variables available in Solidity
  • msg.sender: The address of the sender of the whatever function is being executed.
  • block.timestamp: The current block timestamp as seconds since unix epoch.