Hi Josh,

Based on your second sentence, I'm assuming that you are trying to code an algorithm that goes long and does not borrow any money?

To clarify, The term "go long" means you are holding the stock in expectation that it's price is going to rise, thereby earning a profit.

"Go short" is the opposite, you believe the stock is over-valued and the price is going to fall. If you short a stock, you are borrowing it from your broker to sell - you don't actually have to own the stock. You're hoping to buy the stock back when the price falls, earning a profit. During this window that you're waiting for the stock price to drop, you're paying interest to your broker. When you short a stock you're holding negative shares. You don't own these shares; you borrowed them and need to return them once your position is covered.

So to answer your question,

1. To go long, add the trading guard set_long_only() in the intialize() function of your code.

2. To only use the cash available in your account, add a check in your ordering logic. The example below leaves a 5% cash buffer.

    # If the current price is 1% above the 5-day average price AND we have enough cash, then we will order.  
    if current_price > (1.01 * average_price) and cash > current_price:  
        # Need to calculate how many shares we can buy  
        # Keep 10% of cash available as a buffer  
        number_of_shares = int((0.95*cash) / current_price)  
        # Place the buy order (positive means buy, negative means sell)  
        order(context.security, number_of_shares)  

Also take a look at this thread with a longer explanation: https://www.quantopian.com/posts/negative-cash. Let me know if that helps!

Cheers,
Alisa