#include <iostream>
#include <string>
#include <fstream>

int test() {
   const std::string filename("data.txt");
   std::ifstream fin(filename.c_str());
   if (!fin.good()) {
      std::cerr << "Cannot find file " 
		<< filename << "!" 
		<< std::endl;
      return 1;
   }

   Bool_t haveTrack=kFALSE;
   Bool_t haveWeight=kFALSE;
   Float_t en, wei;

   for (;;) {
      std::string tag;
      fin >> tag;
      if (fin.good())
	 if (tag=="trackin") {
	    fin >> en >> en >> en >> en;
	    haveTrack=kTRUE;
	 } else if (tag=="weight") {
	    fin >> wei >> wei;
	    haveWeight=kTRUE;
	 } else {
	    std::cerr << "Unknown tag \""
		      << tag << "\"!"
		      << std::endl;
	    return 3;
	 }
      else if (fin.eof()) break;
      else {
	 std::cerr << "Cannot read file "
		   << filename << "!"
		   << std::endl;
	 return 2;
      }
      
      if (haveTrack && haveWeight) {
	 std::cout << "log10 of product: ";
	 if (en*wei>0)
	    std::cout << log10(en*wei) 
		      << std::endl;
	 else 
	    std::cout << "ERROR - product "
		      << en*wei << "<0!"
		      << std::endl;
	 haveTrack=haveWeight=kFALSE;
      }
   }
   return 0;
}

   /*
   // you didn't open a file
   FILE* input_file=fopen("data.txt", "r"); 
   
   char line[50] = "trackin";
   char line2[50] = "weight";
   float en_in, f4, en, wei, w2, w3;

   while(!feof(input_file)){

      // you are reading a const char ("%s") into a float.
      // fscanf takes the address of the var it should store the result in.
      fscanf (input_file, "%s",en);
      // you are comparing a string and a float - strcmp takes two const char*s
      if(strcmp (line, en) == 0){
         // pFile[k] is not defined, and you forgot one float,
	 // at least according to your syntax descr:
	 // trackin 0.0 0.0 0.0 0.0
	 // weight 0.0 0.0
	 fscanf (pFile[k],"%*f %*f %f", &f4);

	 en_in = f4;
      }

      // see above
      fscanf (input_file, "%s",wei);

      // see above
      if(strcmp (line2, wei) == 0){

         // see above
	 fscanf (pFile[k],"%*f %f ", &w2);
	 w3 = en_in * w2;
	 w3 = log10(w3);

	 cout<< " EN_IN BEFORE = "<<en_in<<endl;
	 en_in = log10(en_in);
	 cout<< "EN_IN AFTER = "<<en_in<<endl;
      }
   }
   // there is a bracket missing.
   */