Thread: question about pow()

  1. #1
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    question about pow()

    Hello

    Why will the following code output integer c as 0 (null)?

    Code:
    unsigned int c = pow( (double)2 , (double)1000);
    std::cout << c << "\n";
    What would be the proper way of calculating 2^1000 in c++?

    Thanks a lot!

  2. #2
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    An unsigned int is unable to store values larger than 2^32.

    I believe a double would be able to store it. Otherwise you would need a to use a bignum library.

  3. #3
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    Even if a double can store it, it won't be with infinite precision. You will only get a few significant figures.

    If you want the answer with infinite precision, you will have to use a bignum library.

  4. #4
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    Quote Originally Posted by Waterbottle View Post
    An unsigned int is unable to store values larger than 2^32.

    I believe a double would be able to store it. Otherwise you would need a to use a bignum library.
    Actually: (2^32)-1 is the largest you can fit in a 32-bit integer.

    A double should be able to store 1.07E301, which is roughly the value of 2^1000.

    --
    Mats
    Compilers can produce warnings - make the compiler programmers happy: Use them!
    Please don't PM me for help - and no, I don't do help over instant messengers.

  5. #5
    C++まいる!Cをこわせ!
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    Oh and just poking, but in C++, it is really in our best to use the C++ variants of the C functions, std::pow.
    There should be one, no?
    Quote Originally Posted by Adak View Post
    io.h certainly IS included in some modern compilers. It is no longer part of the standard for C, but it is nevertheless, included in the very latest Pelles C versions.
    Quote Originally Posted by Salem View Post
    You mean it's included as a crutch to help ancient programmers limp along without them having to relearn too much.

    Outside of your DOS world, your header file is meaningless.

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