Future Tense--If

If you feel better, you will have to go to school tomorrow.

If you feel better TODAY,<---------It means
if you feel any better today, you will have to go to school tomorrow.



This sentence is more logical.


If + present + future
~~~~~~~~~~~~~~~~~~~~~~

If you feel better TOMORROW, you will have to go to school.

We are talking about what will happen tomorrow here.

We never know WHEN you will feel better.

Let's say you stay at school from 8:30 A.M to noon every day.

What if you feel better at 1 P.M?

You won't need to go to school if you feel better at that time!

It would mean sense if we changed the sentence to
~~~~~~~~~~~~~~~~~~~~~~~~~~~~

If you feel better by 8 A.M tomorrow, you will have to go to school.

( I presume you will need around half an hour to travel from your house to the school.)



What if you feel better at 11 A.M tomorrow?

~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

According to my analysis, I will surely use the first sentence.

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第一句的意思是：
若你明天覺得好些，你就必須上學去
而第二句的意思是：
若你覺得好些，明天你就必須上學去
其實兩句文法都正確，但意思卻不同
從以上例子，你大可以看出，tomorrow的位置不同，有可能改變其意思

希望幫到你！