## main101

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    // main101.cc is a part of the PYTHIA event generator.
    // Copyright (C) 2026 Torbjorn Sjostrand.
    // PYTHIA is licenced under the GNU GPL v2 or later, see COPYING for details.
    // Please respect the MCnet Guidelines, see GUIDELINES for details.

    // Keywords:
    //            Basic usage
    //            Charged multiplicity

    // This is a simple test program. It fits on one slide in a talk.
    // It studies the charged multiplicity distribution at the LHC.

    #include "Pythia8/Pythia.h"
    using namespace Pythia8;
    int main() {
      // Generator. Process selection. LHC initialization. Histogram.
      Pythia pythia;
      pythia.readString("Beams:eCM = 8000.");
      pythia.readString("HardQCD:all = on");
      pythia.readString("PhaseSpace:pTHatMin = 20.");
      // If Pythia fails to initialize, exit with error.
      if (!pythia.init()) return 1;
      Hist mult("charged multiplicity", 100, -0.5, 799.5);
      // Begin event loop. Generate event. Skip if error. List first one.
      for (int iEvent = 0; iEvent < 100; ++iEvent) {
        if (!pythia.next()) continue;
        // Find number of all final charged particles and fill histogram.
        int nCharged = 0;
        for (int i = 0; i < pythia.event.size(); ++i)
          if (pythia.event[i].isFinal() && pythia.event[i].isCharged())
            ++nCharged;
        mult.fill( nCharged );
      // End of event loop. Statistics. Histogram. Done.
      }
      pythia.stat();
      cout << mult;
      return 0;
    }