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You can reduce your headaches as a programmer by writing your programs incrementally.

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"Get something working and keep it working;" that's going to be our mantra.

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Or "Start small and keep it working."

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Here's a program where we're trying to draw a house.

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Rectangle with a triangle on the top,

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and we've done the first part for you. Get something working.

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But I'm now going to try to add to it in a way that says,

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draw more and more of the house and when we make mistakes

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to catch them before there's too much code.

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So we've started with something that is working.

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Bob is going down and turning left.

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Let's complete that square.

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That should be pretty easy to do.

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Just make him turn left again, and go forward.

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You might be tempted to do more lines of code than that,

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but I really recommend testing after you write every little bit of code.

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So let's turn him again,

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and we'll test that,

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and we're going to get to a slightly harder part.

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Now, I want to make him turn this way so that he can finish the house like that.

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So, let me do that.

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Instead of turning left,

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I'm going to have him turn to the right.

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And instead of 90 degrees,

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let's just try going 45 degrees.

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We'll go halfway and then we'll have him go forward by 50 again.

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Oops! This is why it's a good idea to do things a little bit at

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a time because I'm going to get to realize already that I am going the wrong direction.

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So I wanted him to turn to here so that he would go that way but he didn't go far enough.

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He turned 45 degrees but I really needed him to

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go all the way around there, so another 90.

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So I need him to go a 135 degrees.

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That looks a lot better.

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Now I'll just have him turn 90 degrees,

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go forward, and we will have our house.

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Oh no. We don't get a house that way.

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So it turns out that we need to make him not go quite as far.

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So instead of going 50,

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he's got to go a little bit less.

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Maybe he should go 40 each time.

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Almost but not quite.

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You can try just doing trial and error until you get something that's pretty close,

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or sometimes it really helps to step back and do a calculation.

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In this case, the Pythagorean theorem,

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remember that, can really help us.

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We want to make something that is 50

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here and is going to be a right triangle there.

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If we have some length a,

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we need a squared plus a squared to equal 50 squared.

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You could do this in a calculator or you could

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have the Python interpreter work it out for you.

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There is a square root function.

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It's a little tricky,

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you have to import the math module and then we're going to say,

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distance is the square root of 50 times

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50 divided by 2

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and then we will have bob go forward by that distance each time.

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Let's try it and see if we get a nice roof on the house this time.

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Yay.

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So, the main point that I wanted you to take away from this was

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that you're unlikely to get it all

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right the first time if you just write a really long program.

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It's much better to start with something that's working at a line or two,

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test it and make sure that you continue to have a program that is working.

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Build up and always keep your program working.