DorelBarbu's blog

Why using long long fails, but using double gets AC? (when we don't deal with floating point numbers)
By DorelBarbu, history, 8 years ago, In English

Hello, everybody! I was solving http://codeforces.me/contest/319/problem/C which uses the "Convex Hull Trick". After many failed attempts I peeked at the AC solutions.I found a very interesting thing. This gets AC. However, if I replace the explicit conversion to double, with an explicit conversion to long long (which seems more suitable in this case, since we're not dealing with floating point numbers) I get WA, like this. Now, forgive me if it is a dumb question but I really didn't come across something like this before. Can someody help me figure it out? Thank you!

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8 years ago, # |
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cout << (double)1000000000*1000000000 << " " << 1000000000*1000000000 << endl;

Try this and you will understand.

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    8 years ago, # ^ |
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    I believe it's more like

    cout << (double)1000000000*1000000000 << " " << (long long)1000000000*1000000000 << endl;

    Because in the code he's referenced, the instruction was cast to long long on its both sides

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      8 years ago, # ^ |
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      I hope, now it will be better for you.

      long long x = (long long)1e+18;
cout << (double)x*x << " " << (long long)x*x << endl;
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        8 years ago, # ^ |
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        This is indeed much more clearer. Learning by example is great. But what is the exact reason for this? Can a double hold bigger integers than long long?

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        8 years ago, # ^ |
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        Oh thank you!

        That was useful. :D

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