Hello. I'm a little bit puzzeled with differences in this two sentences:

Grammar book says: If I'm going to catch the train, I'll have to leave now. ( We talk about the future)

But if I said : If I'm going to catch the train, I have to leave now. Would the second sentence ( I have to leave now) render the same meaning as for time concerning? In other words, is the second sentence correct?

Thank you.
Hi Olga

You can use either sentence. Using "have to" (rather than "will have to") sounds a bit more urgent/imperative, and thus, in this context, "have to" may be more likely if the speaker is impatient or possibly irritated.

Thank you.
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Can the second sentence be referred as Zero Conditional?
Fandorin, not really. Here is the reference: http://www.englishlanguageguide.com/english/grammar/conditionals.asp
So, I have a doubt because - if you're certain that you won't catch the train in case you don't go now - it can be Zero Conditional because of a strict certainty. Like with cofee on that site. I may be wrong.
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If I am going to catch the train, I have to leave now.
Present: am
Present: have
Therefore, Zero Conditional.
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