Please help me to understand the Code !

[Krish]

Hello! Everybody,
I started to unuderstand the codings in simple_plot example wherein i tried to understand simple.cpp code but had few problems. Those are: -

1.) In this code: -

public:
              SimpleData(double(*y)(double), size_t size):
                        d_size(size),
                        d_y(y)
              {
               }

public:
              SimpleData(double(*y)(double), size_t size):
                        d_size(size),
                        d_y(y)
              {
               }

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Here i came to know that its a constructor with 2 variables, d_size & d_y are declared globally. But main point is i didn't understand " double(*y)(double) " declaration. Also is size_t a new variable introduced in Qwt, if yes what are its limitations?

2.) In this code: -

Const int nPoints=100;
cSin->setData(SimpleData(::sin, nPoints));
cCos->setData(SimpleData(::cos, nPoints));

Const int nPoints=100;
cSin->setData(SimpleData(::sin, nPoints));
cCos->setData(SimpleData(::cos, nPoints));

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Here i came to know that nPoints is an int variable with value=100. Also following 2 lines are setting data for those 2 curves. But main point is what type of arguments are sent here like "::sin" "::cos"& which subroutine is called to set the data actually?

Can anyone please help me out in understanding them.----> I will be obliged.

Thanks in Advance.