problem wth creating a new class

[sweetheartmy smith]

I have to change the class OFDM to SC-FDE.
the head file is

ifndef SCFDE_H

#define SCFDE_H

#include <itpp/base/vec.h>

namespace itpp
{
class SCFDE
{
public:
SCFDE(void) { setup_done = false; }
SCFDE(int inNfft, int inNcp, int inNupsample = 1);
int no_carriers() {return Nfft;}
void set_parameters(const int Nfft, const int Ncp, const int inNupsample = 1);
cvec modulate(const cvec &input);
void modulate(const cvec &input, cvec &output);
cvec demodulate(const cvec &input);
void demodulate(const cvec &input, cvec &output);
private:
double norm_factor;
bool setup_done;
int Nfft, Ncp, Nupsample;
};
} // namespace itpp

endif // #ifndef SCFDE_H

the CPP file is
#include <itpp/comm/SCFDE.h>
#include <itpp/base/specmat.h>
#include <itpp/base/operators.h>
#include <itpp/signal/transforms.h>

namespace itpp
{
SCFDE::SCFDE(int inNfft, int inNcp, int inNupsample)
{
set_parameters(inNfft, inNcp, inNupsample);
}

 void SCFDE::set_parameters(const int inNfft, const int inNcp, const int inNupsample)

{
it_assert(inNfft >= 2, "SCFDE: Nfft must be >=2.");
it_assert(inNcp >= 0 && inNcp <= inNfft, "SCFDE: Ncp must be >=0 and <=Nfft.");
it_assert(inNupsample >= 1 && inNupsample <= 100, "SCFDE: Ncp must be >=1 and <=100.");
Nfft = inNfft;
Ncp = inNcp;
Nupsample = inNupsample;
norm_factor = std::sqrt(static_cast<double>(Nupsample * Nfft * Nfft) / (Nfft + Ncp));
setup_done = true;
}

 void SCFDE::modulate(const cvec &input, cvec &output)

{
it_assert(setup_done == true, "SCFDE::modulate: You must set the length of the FFT and the cyclic prefix!");
const int N = input.length() / Nfft;
it_assert(N*Nfft == input.length(), "SCFDE::modulate: Length of input vector is not a multiple of Nfft.");

output.set_length(Nupsample*N*(Nfft + Ncp));
cvec x(Nfft);

cvec outtemp(Nfft);

for (int i = 0; i < N; i++) {
outtemp = ifft(concat(input.mid(i * Nfft, Nfft / 2), zeros_c(Nfft * (Nupsample - 1)),input.mid(i * Nfft + Nfft / 2, Nfft / 2))) * norm_factor;
x.replace_mid(Nupsample(Nfft + Ncp)i, concat(outtemp.right(Nupsample*Ncp), outtemp));
cvec output = fft(output.mid(Nupsample * (i * (Nfft + Ncp) + Ncp), Nupsample * Nfft));
}
}

 cvec SCFDE::modulate(const cvec &input)

{
cvec output;
modulate(input, output);
return output;
}

 void SCFDE::demodulate(const cvec& input, cvec &output)

{
it_assert(setup_done == true, "SCFDE::demodulate: You must set the length of the FFT and the cyclic prefix!");
const int N = input.length() / (Nfft + Ncp) / Nupsample;
it_assert(NupsampleN(Nfft + Ncp) == input.length(), "SCFDE: Length of input vector is not a multiple of Nfft+Ncp.");

output.set_length(N*Nfft);
// normalize also taking the energy loss into the cyclic prefix into account
for (int i = 0; i < N; i++) {

output.replace_mid(Nfft*i, concat(input.left(Nfft / 2), input.right(Nfft / 2)) / norm_factor);
}
}

cvec SCFDE::demodulate(const cvec &input)
{
cvec output;
demodulate(input, output);
return output;
}

} //namespace itpp

But there are errors

error1: MSVCRT.lib(crtexe.obj) : error LNK2001: unresolved external symbol _main

error2: >F:\huzhe\new SC\SCFDE\Release\SCFDE.exe : fatal error LNK1120: 1 unresolved external command

why?