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POC++ Adding big numbers together with operator overload
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  1. POC++ Adding big numbers together with operator overload
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    copied!<p>I am new to C++ and attempting to create a "BigInt" class. I decided to base most of the implementation on reading the numbers into vectors.</p> <p>So far I have only written the copy constructor for an input string. </p> <pre><code>Largenum::Largenum(std::string input) { for (std::string::const_iterator it = input.begin(); it!=input.end(); ++it) { number.push_back(*it- '0'); } } </code></pre> <p>The problem I am having is with the addition function. I have created a function which seems to work after I tested it a few times, but as you can see its highly inefficient. I have 2 different vectors such as:</p> <pre><code>std::vector&lt;int&gt; x = {1,3,4,5,9,1}; std::vector&lt;int&gt; y = {2,4,5,6}; </code></pre> <p>The way I thought to solve this problem was to add 0s before the shorter, in this case y vector to make both vectors have the same size such as:</p> <pre><code>x = {1,3,4,5,9,1}; y = {0,0,2,4,5,6}; </code></pre> <p>Then to add them using elementary style addition. </p> <p>I don't want to add 0s infront of vector Y as it would be slow with a large number. My current solution is to reverse the vector, then push_back the appropriate amount of 0s, then reverse it back. This may be slower then simply inserting at the front it seems, I have not tested yet.</p> <p>The problem is that after I do all of the addition on the vectors and push_back the result. I am left with a backward vector and I need to use reverse yet again! There has got to be a much better way then my method but I am stuck on finding it. Ideally I would make A const as well. Here is the code of the function:</p> <pre><code>Largenum Largenum::operator+(Largenum &amp;A) { bool carry = 0; Largenum sum; std::vector&lt;int&gt;::size_type max = std::max(A.number.size(), this-&gt;number.size()); std::vector&lt;int&gt;::size_type diff = std::abs (A.number.size()-this-&gt;number.size()); if (A.number.size()&gt;this-&gt;number.size()) { std::reverse(this-&gt;number.begin(), this-&gt;number.end()); for (std::vector&lt;int&gt;::size_type i = 0; i&lt;(max-diff); ++i) this-&gt;number.push_back(0); std::reverse(this-&gt;number.begin(), this-&gt;number.end()); } else if (this-&gt;number.size() &gt; A.number.size()) { std::reverse(A.number.begin(), A.number.end()); for (std::vector&lt;int&gt;::size_type i = 0; i&lt;(max-diff); ++i) A.number.push_back(0); std::reverse(A.number.begin(), A.number.end()); } for (std::vector&lt;int&gt;::size_type i = max; i!=0; --i) { int num = (A.number[i-1] + this-&gt;number[i-1] + carry)%10; sum.number.push_back(num); (A.number[i-1] + this-&gt;number[i-1] + carry &gt;= 10) ? carry = 1 : carry = 0; } if (carry) sum.number.push_back(1); reverse(sum.number.begin(), sum.number.end()); return sum; } </code></pre> <p>If anyone has any input that would be great, this is my first program using classes in C++ and its fairly overwhelming. </p>
 

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