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pragma solidity ^0.5.0; | |
contract ERC20 { | |
using SafeMath for uint256; | |
event Approval(address indexed tokenOwner, address indexed spender, uint tokens); | |
event Transfer(address indexed from, address indexed to, uint tokens); | |
mapping(address => uint256) balances; | |
mapping(address => mapping (address => uint256)) allowed; | |
string public symbol; | |
uint8 public decimals; | |
string public name; | |
uint256 private _totalSupply; | |
constructor(uint8 _decimals, string memory _symbol, string memory _name, uint256 _total_supply) public{ | |
decimals = _decimals; | |
symbol = _symbol; | |
name = _name; | |
_totalSupply = _total_supply; | |
balances[msg.sender] = _totalSupply; | |
} | |
function totalSupply() public view returns (uint256) { | |
return _totalSupply; | |
} | |
function balanceOf(address tokenOwner) public view returns (uint) { | |
return balances[tokenOwner]; | |
} | |
function transfer(address receiver, uint numTokens) public returns (bool) { | |
require(numTokens <= balances[msg.sender]); | |
balances[msg.sender] = balances[msg.sender].sub(numTokens); | |
balances[receiver] = balances[receiver].add(numTokens); | |
emit Transfer(msg.sender, receiver, numTokens); | |
return true; | |
} | |
function approve(address delegate, uint numTokens) public returns (bool) { | |
allowed[msg.sender][delegate] = numTokens; | |
emit Approval(msg.sender, delegate, numTokens); | |
return true; | |
} | |
function allowance(address owner, address delegate) public view returns (uint) { | |
return allowed[owner][delegate]; | |
} | |
function transferFrom(address owner, address buyer, uint numTokens) public returns (bool) { | |
require(numTokens <= balances[owner]); | |
require(numTokens <= allowed[owner][msg.sender]); | |
balances[owner] = balances[owner].sub(numTokens); | |
allowed[owner][msg.sender] = allowed[owner][msg.sender].sub(numTokens); | |
balances[buyer] = balances[buyer].add(numTokens); | |
emit Transfer(owner, buyer, numTokens); | |
return true; | |
} | |
} | |
library SafeMath { | |
function sub(uint256 a, uint256 b) internal pure returns (uint256) { | |
assert(b <= a); | |
return a - b; | |
} | |
function add(uint256 a, uint256 b) internal pure returns (uint256) { | |
uint256 c = a + b; | |
assert(c >= a); | |
return c; | |
} | |
} |
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