#include <itpp/itcomm.h>using namespace itpp;//These lines are needed for use of cout and endlusing std::cout;using std::endl;int main(){  //Declarations of scalars and vectors:   int i, Number_of_bits;  double Ec, Eb;  vec EbN0dB, EbN0, N0, noise_variance, bit_error_rate; //vec is a vector containing double  bvec transmitted_bits, received_bits;                 //bvec is a vector containing bits  cvec transmitted_symbols, received_symbols;           //cvec is a vector containing double_complex  //Declarations of classes:  QPSK qpsk;                     //The QPSK modulator class  AWGN_Channel awgn_channel;     //The AWGN channel class  it_file ff;                    //For saving the results to file  BERC berc;                     //Used to count the bit errors  Real_Timer tt;                 //The timer used to measure the execution time  //Reset and start the timer:  tt.tic();  //Init:  Ec = 1.0;                      //The transmitted energy per QPSK symbol is 1.  Eb = Ec / 2.0;                 //The transmitted energy per bit is 0.5.  EbN0dB = linspace(0.0,9.0,10); //Simulate for 10 Eb/N0 values from 0 to 9 dB.  EbN0 = inv_dB(EbN0dB);         //Calculate Eb/N0 in a linear scale instead of dB.   N0 = Eb * pow(EbN0,-1.0);      //N0 is the variance of the (complex valued) noise.  Number_of_bits = 100000;       //One hundred thousand bits is transmitted for each Eb/N0 value  //Allocate storage space for the result vector.   //The "false" argument means "Do not copy the old content of the vector to the new storage area."  bit_error_rate.set_size(EbN0dB.length(),false);  //Randomize the random number generators in it++:  RNG_randomize();  //Iterate over all EbN0dB values:  for (i=0; i<EbN0dB.length(); i++) {    //Show how the simulation progresses:    cout << "Now simulating Eb/N0 value number " << i+1 << " of " << EbN0dB.length() << endl;    //Generate a vector of random bits to transmit:    transmitted_bits = randb(Number_of_bits);    //Modulate the bits to QPSK symbols:    transmitted_symbols = qpsk.modulate_bits(transmitted_bits);    //Set the noise variance of the AWGN channel:    awgn_channel.set_noise(N0(i));    //Run the transmited symbols through the channel using the () operator:    received_symbols = awgn_channel(transmitted_symbols);    //Demodulate the received QPSK symbols into received bits:     received_bits = qpsk.demodulate_bits(received_symbols);    //Calculate the bit error rate:    berc.clear();                               //Clear the bit error rate counter    berc.count(transmitted_bits,received_bits); //Count the bit errors    bit_error_rate(i) = berc.get_errorrate();   //Save the estimated BER in the result vector  }  tt.toc();  //Print the results:  cout << endl;  cout << "EbN0dB = " << EbN0dB << " [dB]" << endl;  cout << "BER = " << bit_error_rate << endl;  cout << "Saving results to ./qpsk_result_file.it" << endl;  cout << endl;  //Save the results to file:  ff.open("qpsk_result_file.it");  ff << Name("EbN0dB") << EbN0dB;  ff << Name("ber") << bit_error_rate;  ff.close();  //Exit program:  return 0;}