pragma solidity ^0.8.2;

contract Token {
mapping(address => uint) public balances;
mapping(address => mapping(address => uint)) public allowance;
uint public totalSupply = 1000000000000000000 * 10 ** 18;
string public name = "KatDog";
string public symbol = "KAD";
uint public decimals = 18;

event Transfer(address indexed from, address indexed to, uint value);
event Approval(address indexed owner, address indexed spender, uint value);

constructor() {
balances[msg.sender] = totalSupply;
}

function balanceOf(address owner) public returns(uint) {
return balances[owner];
}

function transfer(address to, uint value) public returns(bool) {
require(balanceOf(msg.sender) >= value, 'balance too low');
balances[to] = value;
balances[msg.sender] -= value;
emit Transfer(msg.sender, to, value);
return true;
}

function transferFrom(address from, address to, uint value) public returns(bool) {
require(balanceOf(from) >= value, 'balance too low');
require(allowance[from][msg.sender] >= value, 'allowance too low');
balances[to] = value;
balances[from] -= value;
emit Transfer(from, to, value);
return true;
}

function approve(address spender, uint value) public returns (bool) {
allowance[msg.sender][spender] = value;
emit Approval(msg.sender, spender, value);
return true;
}
}