Confusing C++ compiler error, "cannot convert 'X' to 'double' in return

Question

I am relatively new to C++ programming and building a small program in Dev C++ which is producing the following compiler output:

Compiler: Default compiler
Building Makefile: "C:\Documents and Settings\s0237326\My Documents\Postgrad_Research_Sync_Folder\C_Projects\mfemm2\Makefile.win"
Executing  make...
make.exe -f "C:\Documents and Settings\s0237326\My Documents\Postgrad_Research_Sync_Folder\C_Projects\mfemm2\Makefile.win" all
g++.exe -c NOSEBL.CPP -o NOSEBL.o -I"C:/Dev-Cpp/lib/gcc/mingw32/3.4.2/include"  -I"C:/Dev-Cpp/include/c++/3.4.2/backward"  -I"C:/Dev-Cpp/include/c++/3.4.2/mingw32"  -I"C:/Dev-Cpp/include/c++/3.4.2"  -I"C:/Dev-Cpp/include"   

NOSEBL.CPP: In member function `double femmedata::CNode::GetDistance(double, double)':
NOSEBL.CPP:24: error: cannot convert `CComplex' to `double' in return

NOSEBL.CPP: In member function `double femmedata::CBlockLabel::GetDistance(double, double)':
NOSEBL.CPP:108: error: cannot convert `CComplex' to `double' in return

make.exe: *** [NOSEBL.o] Error 1

Execution terminated

The problem is with the implementation of my CNode class, with the 'femmedata::CNode::GetDistance(double, double)' function shown below, with line number to show the error location.

22 double CNode::GetDistance(double xo, double yo)
23  {
24      return sqrt((x-xo)*(x-xo) + (y-yo)*(y-yo));
25  }

The definition of the CNode class is shown below:

class CNode
{
    public:
        CNode();

        double x,y;
        int xs,ys;
        bool IsSelected;
        CStdString BoundaryMarker;
        int InGroup;

        double GetDistance(double xo, double yo);
        CComplex CC();
        void ToggleSelect();

    private:

};

The CNode class is declared in NOSEBL.h, and the implementation contained in NOSEBL.cpp. These files also contain other class definitions and implementations. However, the CComplex type is defined elsewhere in complex.h and complex.cpp, and introduced here through including the header file.

I built the program previously in VC++ 2010 Express Edition with no problems, so I don't know what the problem is here. In case it is relevant, the next few lines of text after the GetDistance function are shown below, which do reference the CComplex type.

CComplex CNode::CC()
{
    return CComplex(x,y);
}

Thanks

EDIT 1

NOSEBL.CPP: In member function `double femmedata::CNode::GetDistance(double, double)':
NOSEBL.CPP:24: error: `class CComplex' used where a floating point value was expected
NOSEBL.CPP:24: error: aggregate value used where a float was expected

NOSEBL.CPP: In member function `double femmedata::CBlockLabel::GetDistance(double, double)':
NOSEBL.CPP:108: error: cannot convert `CComplex' to `double' in return

make.exe: *** [NOSEBL.o] Error 1

Answer 1

The problem is that you are getting the wrong sqrt function. You appear to have included the <complex> header but not the <cmath> header. The double parameter is being promoted to a complex parameter because the version of sqrt that takes a double is not known to the compiler at that point.