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PO'Invalid use of void expression' passing arguments of functions
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  1. PO'Invalid use of void expression' passing arguments of functions
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    copied!<p>This is a piece of my code that solves systems of differential equations.</p> <pre><code>Vector dydx(Neq); void DiffEq(Vector x, Vector &amp;dydx) { dydx(0) = x(1); dydx(1) = -x(0); } double MidPoint(int n, Vector x) { double h=H/n; Matrix z(n+1,n+1); z.fillRow(0,x); DiffEq(x, dydx); z.fillRow(1,AddVec(x, dydx*h)); //Error: Invalid use of void expression for (int j=1; j&lt;n; j++) { DiffEq(z.getRow(j), dydx); z.fillRow(j+1, AddVec(z.getRow(j-1), dydx*h*2)); //error: void value not ignored as it ought to be } DiffEq(z.getRow(n), dydx); return 0.5*AddVec(z.getRow(n), z.getRow(n-1), dydx*h); //Error: Invalid use of void expression } </code></pre> <p>The classes Vector and Matrix are custom. This is Vector</p> <pre><code>class Vector { public: Vector(size_t size): vSize(size), vData(size){} int getSize(){return vSize;} double&amp; operator()(size_t i){return vData[i];} double operator()(size_t i) const {return vData[i];} void operator+(double d) // These only overload the Vector + int operator { for (int i=0; i&lt;vSize; i++) {vData[i]=vData[i]+d;} } void operator*(double d) { for (int i=0; i&lt;vSize; i++) {vData[i]=vData[i]*d;} } size_t vSize; vector&lt;double&gt; vData; }; </code></pre> <p>With a function</p> <pre><code>Vector AddVec(Vector v1, Vector v2) { Vector totVec(v1.getSize()); for (int i=0; i&lt;v1.getSize(); i++) {totVec(i) = v1(i) + v2(i);} return totVec; } </code></pre> <p>And the same function for 3 vectors.</p> <p>Now I realise that the error means that I'm passing void to some function, but I cannot figure out where things go wrong. When I try writing a test program, everything seems to work fine. </p>
 

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