Dynamic array question

This is a discussion on Dynamic array question within the C++ Programming forums, part of the General Programming Boards category; How to write functions to add 2 big integers with dynamic arrays? The 2 integers are input by users. 2 ...

  1. #1
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    Dynamic array question

    How to write functions to add 2 big integers with dynamic arrays?
    The 2 integers are input by users.
    2 integer arrays store the input such that :
    x[0]=number of digits
    x[1]=1 st digit of the integer input (starting from the right)
    x[2]=2 nd digit of the integer input
    ... & so on
    eg.
    input integer 1: 456
    x[0]=3
    x[1]=6
    ...

    There is function to store the input:
    void input(int*);
    Another takes the 2 integer arrays as parameter to add the integers.
    int *add(int *,int*);

    How to divide the input integers into digits?
    If I know how to write void input(int*), then I may know how to write int *add(int *,int*)
    Anyone can help? Any similar example on the net that can inspire me?
    Last edited by Roy01; 12-10-2006 at 07:19 AM.

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    Could you please be more specific?

  3. #3
    and the hat of wrongness Salem's Avatar
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    I can see that you might store 5 in x[0] representing the length, but what would you store in x[1]?
    Would it be '1', the first digit of input?
    Would it be '9', the least significant value of the input?

    > how to divide the input integer into digits
    It's a lot easier if you read it as a string, expecially if you're considering very long input.

    The rest is just modelling how you would add two numbers on paper
    - start at the right, and add with carry your way to the left.
    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.
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    Quote Originally Posted by Salem
    If you type in
    13579

    I can see that you might store 5 in x[0] representing the length, but what would you store in x[1]?
    Would it be '1', the first digit of input?
    Would it be '9', the least significant value of the input?

    > how to divide the input integer into digits
    It's a lot easier if you read it as a string, expecially if you're considering very long input.

    The rest is just modelling how you would add two numbers on paper
    - start at the right, and add with carry your way to the left.
    Oops,I forgot to mention that, sorry.
    It should be reverse so x[1] should be 9 according to your example.
    If string can't be used, how to divide the integer into digits?
    I asked this question as it is given that the function to store the input:
    void input(int*);
    takes an integer as parameter.
    Last edited by Roy01; 12-10-2006 at 07:17 AM.

  5. #5
    and the hat of wrongness Salem's Avatar
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    Well you extract digits from an integer using /10 and %10 operations in some kind of loop.
    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.
    I support http://www.ukip.org/ as the first necessary step to a free Europe.

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    Thanks, I always forget this.

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    The magic phrase you're looking for is "arbitrary precision arithmetic". It's implemented by the GNU MP library - see

    http://www.swox.com/gmp/

    and if you just want to use it rather than compile code for it, there are a number of implementations including Maxima, an open-source descendent of MACSYMA:

    http://maxima.sourceforge.net/

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    Thanks, these are quite useful for me.

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