Thread: Question..

  1. #1
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    Unhappy Question..

    How do I use the pow command?

    I need to basicly do 10^x

    I dont know how to do it with the pow command if any one could help me I would be thankful

  2. #2
    and the hat of int overfl Salem's Avatar
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    <batman>
    pow!!!!
    zap!!!!
    </batman>

    > How do I use the pow command?
    Read the manual page, follow the examples?
    n = pow(x, y);
    If you dance barefoot on the broken glass of undefined behaviour, you've got to expect the occasional cut.
    If at first you don't succeed, try writing your phone number on the exam paper.

  3. #3
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    >How do I use the pow command?
    Code:
    double answer = pow(10., x)

  4. #4
    (?<!re)tired Mario F.'s Avatar
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    Code:
    double pow( double base, double exp );
    As such,

    Code:
    double result;
    double exp = 3; // for instance
    
    result = pow(10.0, exp);
    Do NOT use integers with this function. The standard states that implementations are free to overload floating-point functions to their float, double and long double types. So, its possible that your implementation has pow defined as:

    double pow( float base, float exp );
    double pow( double base, double exp );
    double pow( long double base, long double exp );


    If you use an integer as an argument to one or both parameters, the compiler will complain your attempt is ambiguous. Even if it does not (because some compilers do not overload or provide preprocessor policies), your code may fail to compile on other implementations.
    Originally Posted by brewbuck:
    Reimplementing a large system in another language to get a 25% performance boost is nonsense. It would be cheaper to just get a computer which is 25% faster.

  5. #5
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    >Do NOT use integers with this function.
    Doesn't C++ have a:
    Code:
    double pow( double base, int exp );
    I have no idea how to check this. Maybe the C++ standard has a list?

  6. #6
    MFC killed my cat! manutd's Avatar
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    If you need to do ints, just write it all out:
    Code:
    x = x*x*x*x*x*x*x*x*x*x      //x^10
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  7. #7
    (?<!re)tired Mario F.'s Avatar
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    Quote Originally Posted by manutd
    If you need to do ints, just write it all out:
    Code:
    x = x*x*x*x*x*x*x*x*x*x      //x^10
    You are joking right?
    Originally Posted by brewbuck:
    Reimplementing a large system in another language to get a 25% performance boost is nonsense. It would be cheaper to just get a computer which is 25% faster.

  8. #8
    MFC killed my cat! manutd's Avatar
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    Yes.
    Silence is better than unmeaning words.
    - Pythagoras
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  9. #9
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    I checked the library for Dev-C++ and it does have a:
    Code:
    double pow( double base, int exp );
    I dunno if it's standard though.

  10. #10
    Lurking whiteflags's Avatar
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    It's not. I don't understand why you can't just use a cast to double for intermediate use of pow() though.

  11. #11
    (?<!re)tired Mario F.'s Avatar
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    As citizen said. It's not a big deal to use a cast in this situation. Cast to whatever floating-point type is more appropriate, adorn the literal or define floating-point variables, do what you must. But avoid using integers even if your compiler happily says everything is alright
    Originally Posted by brewbuck:
    Reimplementing a large system in another language to get a 25% performance boost is nonsense. It would be cheaper to just get a computer which is 25% faster.

  12. #12
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    >It's not.
    Do you have a copy of the C++ standard to verify that? Because I'm fairly certain it's in there.

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    >But avoid using integers even if your compiler happily says everything is alright
    I see no reason to avoid using int for the exponent. Unless you're compiling C code.

  14. #14
    Lurking whiteflags's Avatar
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    > Do you have a copy of the C++ standard to verify that?
    I can find a reference.
    http://www.dinkumware.com/manuals/?m...=math.html#pow
    Barring you don't trust that, various implementations will let you know what is available by extention if you look it up in the help files.

  15. #15
    (?<!re)tired Mario F.'s Avatar
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    Well... the standard does in fact state the following signatures for pow (26.5.6):

    float pow(float, int)
    float pow(float, float)
    double pow(double, int)
    double pow(double, double)
    long double pow(long double, int)
    long double pow(long double, long double)

    So yes, an int exponent will not generate ambiguity.
    Originally Posted by brewbuck:
    Reimplementing a large system in another language to get a 25% performance boost is nonsense. It would be cheaper to just get a computer which is 25% faster.

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