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POhow to make a copy of a variable in c++
 

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  1. POhow to make a copy of a variable in c++
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    <pre><code>#include &lt;iostream&gt; #include &lt;math.h&gt; using namespace std; class polynomial{ int degree; float *coefs; public: polynomial(int d); float operator()(float x); void operator==(polynomial P); polynomial operator^(int k); float operator[](float x); float *getcoefs(); }; polynomial::polynomial(int d){ int i; degree=d; if(d&gt;=0){ coefs=(float *)malloc((d+1)*sizeof(float)); cout&lt;&lt;"Create a polynomial of degree "&lt;&lt;d&lt;&lt;"\n"; for (i=d;i&gt;0;i--){ cout&lt;&lt;"The coefficient of x^"&lt;&lt;i&lt;&lt;" is : "; cin&gt;&gt;coefs[i]; cout&lt;&lt;"\n"; } cout&lt;&lt;"The constant is : "; cin&gt;&gt;coefs[0]; cout&lt;&lt;"\n"; cout&lt;&lt;"The polynomial is created\n"; } } </code></pre> <p>This is an overloading of the () operator so that P(x) returns the value of the polynomial:</p> <pre><code>float polynomial::operator()(float x){ float sum=0; int i,kstart; for(i=0;i&lt;=degree;i++){ if(coefs[i]!=0){ kstart=i; break; } } for(i=kstart;i&lt;=degree;i++){ sum+=coefs[i]*pow(x,i-kstart); } return sum; } </code></pre> <p>This is an overloading of the == that is copying the coefficients of one polynomial to another's:</p> <pre><code>void polynomial::operator==(polynomial P){ coefs=P.coefs; } </code></pre> <p>This is an overloading of the ^ so that P^k returns the k-th derivative of P:</p> <pre><code>polynomial polynomial::operator^(int k){ int i,j; polynomial G(-1); G.degree=this-&gt;degree; G==(*this); if(k&gt;G.degree){ for(i=0;i&lt;=G.degree;i++){ G.coefs[i]=0; } } else{ for(i=0;i&lt;k;i++){ G.coefs[i]=0; for(j=i+1;j&lt;=G.degree;j++){ G.coefs[j]*=(j-i); } } } return G; } float polynomial::operator[](float x){ return (x-(*this)(x)/(((*this)^1)(x))); } float *polynomial::getcoefs(){ return coefs; } int main(){ int i,d,maxiter,found; float seed,x1,x2,e; float *coefs; cout&lt;&lt;"The polynomial's degree is : "; cin&gt;&gt;d; cout&lt;&lt;"\n"; polynomial P(d),temp(-1); cout&lt;&lt;"-------Solve P(x)=0--------\n"; cout&lt;&lt;"Maxiterations = "; cin&gt;&gt;maxiter; cout&lt;&lt;"\n"; cout&lt;&lt;"Tolerance = "; cin&gt;&gt;e; cout&lt;&lt;"\n"; cout&lt;&lt;"Seed = "; cin&gt;&gt;seed; cout&lt;&lt;"\n"; found=0; x1=seed; for(i=0;i&lt;maxiter;i++){ memcpy((void *)(&amp;temp),(void *)(&amp;P),sizeof(polynomial)); x2=P[x1]; if(fabs(x2-x1)&lt;=e){ found=1; break; } coefs=temp.getcoefs(); cout&lt;&lt;coefs[0]&lt;&lt;"\n"; cout&lt;&lt;coefs[1]&lt;&lt;"\n"; cout&lt;&lt;coefs[2]&lt;&lt;"\n"; x1=x2; } if(found==1){ cout&lt;&lt;"A possible solution is x = "&lt;&lt;x2&lt;&lt;"\n"; } else{ cout&lt;&lt;"No solution found!\n"; } system("PAUSE"); return EXIT_SUCCESS; } </code></pre> <p>The problem can be seen in these testing lines:</p> <pre><code>cout&lt;&lt;coefs[0]&lt;&lt;"\n"; cout&lt;&lt;coefs[1]&lt;&lt;"\n"; cout&lt;&lt;coefs[2]&lt;&lt;"\n"; </code></pre> <p>The coefficients should stay the same,but now they change</p>
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    1. COTrack down whoever created a _void_ `operator==` with _side effects_, and punch them soundly in the head.
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      1. POhow to make a copy of a variable in c++
      1. USHenning Makholm
    2. COGotta hand it to Henning. Operator overloading is usually a can of worms, and this particular case of overloading... argh!
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      1. POhow to make a copy of a variable in c++
      1. USRonaldBarzell
    3. COI know,the prof is old and stubborn and we all hate him...But any ideas?
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