Thread: C++ prog help

Hey. I did a program that reads a file which contains names of students in a class. The names of the students are then used to read files which contain each students' grades. I then had to calculate the average of each individual student, then also calculate the average of the class and the max score and the min score of the class (not meaning the average, but each individual grade). My average isn't calculating right. It is off by a couple hundredths and I can't figure out why. Would anyone be willing to help? Thanks. Here's my code:

Code:

# include <iostream>
# include <fstream>
# include <cstdlib>
# include <string>
# include <iomanip>

using namespace std;

int main()
{
         double w = -1;
		 string fileName, firstName, lastName, middleInitial, studName;
		 double countStud = 0, countSpaces = 0, x = 0;
		 double count = 0, min = 101, max = 0;
		 double classavg = 0;
	     double sum = 0;

		 cout << "Enter the name of the student file: ";
		 cin  >> fileName;
		 cout << endl;
		 
         ifstream inData;
         inData.open(fileName.c_str());
         if (!inData)
             cout << "File doesn't exist!" << endl;
         else
         {
			 cout << "First\tMI  Last\t\tAverage\n" << endl;
             
             while (inData.good())
             {
                   inData >> lastName
                          >> firstName
                          >> middleInitial;
                   studName = firstName + lastName + ".dat";       
                   count = 0; w = -1; sum = 0;
                   
                   ifstream inData2;
                   inData2.open(studName.c_str());
                   if (!inData2)
                      cout << firstName 
                           << "\t" 
                           << middleInitial
                           << "  " 
                           << lastName 
                           << "\t\tNO DATA FILE" 
                           << endl;
                   else
                       while (inData2.good())
                       {
                             inData2 >> w;

        	                 if (w != -1)
        			         {
                                   count++;
				                   if (min > w) min = w;
				                   if (max < w) max = w;
                             }
			                 sum += w;
                       }
                    inData2.close();
                    inData2.clear();
                    
		            if (count == 0) cout << firstName 
                                      << "\t" 
                                      << middleInitial 
                                      << "  " 
                                      << lastName
                                      << "\t" 
                                      << "NO GRADES" 
                                      << endl;
                  	else
		            {
			            sum = sum / count;
					    classavg += sum;
					    countStud++;
					    cout << firstName 
                             << "\t" 
                             << middleInitial
                             << "  " 
                             << lastName 
                             << "\t\t" 
                             << fixed << setprecision(2) << sum 
                             << endl;
                    }
             }
             
             inData.close();
             inData.clear();
             
			 classavg = classavg / countStud;
		
			 cout << endl;
			 cout << endl;
             cout << "Max Grade = " 
                  << fixed 
                  << setprecision(2) 
                  << max 
                  << endl;
			 cout << "Min Grade = " 
                  << fixed 
                  << setprecision(2) 
                  << min 
                  << endl;
             cout << endl;
             cout << "Class Average = " 
                  << fixed 
                  << setprecision(2) 
                  << classavg;
         }         
         

       	 char d;
		 cin >> d;
		 return 0;
}

>> while (inData.good())
By doing this, you are likely using the last piece of data twice. The next line reads in a last name, but the file stream won't fail until your attempt to read in that last name fails. That means one extra iteration of the loop will run just re-using the data from the previous run.

The solution is to use the return value of the read as the control for the loop (e.g. while (inData >> lastName)), or check the state of the stream after the first read attempt and then break the loop.