pragma solidity ^0.5.2;

contract coin {

// maximum count of coins available for sale

uint public max_coin = 1000000;

// Introducing USD to coin conversion rate

uint public usd_to_coin = 1000;

// Introducing total number of coins bought by the investors

uint public total_coin_bought = 0;

// Mapping investors address to equity and USD

mapping(address => uint) equity_coins;

mapping(address => uint) equity_usd;

//checking if investors can buy coins

modifier can_buy_coin (uint usd_invested) {

require (usd_invested * usd_to_coin + total_coin_bought <= max_coin);

_;

}

//getting equity in coins

function equity_in_coins(address investor) external view returns (uint) {

return equity_coins[investor];

}

// getting equity in usd

function equity_in_usd(address investor) external view returns (uint) {

return equity_usd[investor];

}

// Buying coins

function buy_coins(address investor, uint usd_invested) external

can_buy_coin (usd_invested) {

uint coins_bought = usd_invested * usd_to_coin;

equity_coins[investor] += coins_bought;

equity_usd[investor] = equity_coins[investor] / 1000;

total_coin_bought += coins_bought;

}

// Buying coins

function sell_coins(address investor, uint coins_sold) external {

equity_coins[investor] - coins_sold;

equity_usd[investor] = equity_coins[investor] / 1000 ;

total_coin_bought -= coins_sold;

}

}