Error while instantiating an object without inheritance - c++

Question

So far I was using classes inheriting from other classes, now I had the need to creating a class inheriting from anything. I called it from my client class and I'm getting error that doesn't make sense to me. what am I doing wrong?
MathHelp .h
public:
float addPerc(float whole, float perc);
float subPerc(float whole, float perc);
MathHelp .cpp
float addPerc(float whole, float perc)
{
return 0;
}
float subPerc(float whole, float perc)
{
return 0;
}
calling from client
MathHelp* mathHelp = new MathHelp();
float mathResult = mathHelp->addPerc(100,5);
Error:
error LNK2019: unresolved external symbol "public: float __thiscall MathHelp::addPerc(float,float)" (?addPerc#MathHelp##QAEMMM#Z)
referenced in function "public: virtual void __thiscall EnergyManager::draw(class cocos2d::Renderer *,class cocos2d::Mat4 const &,unsigned int)" (?draw#EnergyManager##UAEXPAVRenderer#cocos2d##ABVMat4#3#I#Z)

Answer 1

Method declarations need to also have the name of the class when you're declaring them outside of the class definition.
float MathHelp::addPerc(float whole, float perc)
{
return 0;
}
float MathHelp::subPerc(float whole, float perc)
{
return 0;
}

Answer 2

With the code that has been provided, if they are taken as they directly appear in the files, you are missing the scope for the methods of the class MathHelp, you'd instead want to try something like this:
float MathHelp::addPerc(float whole, float perc)
{
return 0;
}
float MathHelp::subPerc(float whole, float perc)
{
return 0;
}