Operator Precedence problem in Shunting Yard Algo

[Hallett-K]

In the Shunting Yard Algorithm video, we give + a higher precedence than -. Whilst this is usually fine, there's an issue here.

Consider the expression 1 - 2 + 3. Mathematically, if we were to add then subtract, what we want to be doing is -2 + 3. What the code does in this case instead is 2 + 3. This means that we end up doing 1 - 5, rather than 1 + 1, which is incorrect.

The easiest solution would be to give + and - the same precedence, and for the sake of consistency also give * and / the same precedence. Alternatively we'd need to check whether the first parameter is part of a subtraction, which can be a little finnicky.

[quincy451]

I noticed this also...but I have a different explaination of how it should be:1-2+3 if + and - are the same precedence level which is consistent with what I was taught but not the video.evualating left to right I get1-2 = -1then -1+3 = 2 again. interested in Javid's view. On Sunday, May 5, 2024 at 10:13:50 AM CDT, Krystal Hallett ***@***.***> wrote: In the Shunting Yard Algorithm video, we give + a higher precedence than -. Whilst this is usually fine, there's an issue here. Consider the expression 1 - 2 + 3. Mathematically, if we were to add then subtract, what we want to be doing is -2 + 3. What the code does in this case instead is 2 + 3. This means that we end up doing 1 - 5, rather than 1 + 1, which is incorrect. The easiest solution would be to give + and - the same precedence, and for the sake of consistency also give * and / the same precedence. Alternatively we'd need to check whether the first parameter is part of a subtraction, which can be a little finnicky. — Reply to this email directly, view it on GitHub, or unsubscribe. You are receiving this because you are subscribed to this thread.Message ID: ***@***.***>