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calculate avg from input file

angrybeaver76 (21)
Hi. I have this program I'm writing that I'm stuck on. The first part needs to read in a list of student ID's and a corresponding test score (example input file below). Scores are int values between 1-10. A student that did not take the test will have a -1 score and should not be counted towards the average.

Example input file:
1234 1
3456 3
3453 5
4365 9
3456 -1

I was able to figure out this code to calculate the average from reading in a file. See below.

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

using namespace std;

int main()
{ 
    ifstream inputFile;    
    int score, avg, numofstudents = 0, totalgrade = 0;
    string id, grade;
    
    inputFile.open("TestScores.txt");
    
    //get the average
    while (!inputFile.eof())
    {
          inputFile >> id;
          cout << left << setw(10) << id;
          inputFile >> score;
          cout << left << setw(10) << score << endl;
          
          if (score >= 0 && score <= 10)
          {
               totalgrade = totalgrade + score;
               numofstudents++;
          }     
          
    }
    
    avg = totalgrade/numofstudents;
    
    cout << "The avg score is " << avg << endl << endl;


Where I'm stuck is the next part of the program. I need to create a new output file that has a new column with the converted letter grade. So I need to take the average from the first part above and generate the letter grade. (-1 gets no grade, average or the average + 1 = B, average + 2 or average + 3 = A-, +4 ( or 10 if average is 7 or more ) = A, average -1 = C and average – 2 or less = F.)


Needed output file:
1234 1 F
3456 3 C
3453 5 B
4365 9 A
3456 -1


I started with this... but then I stopped short cause I don't think a switch is the way to go. I can't figure out the best way to go about this. Any suggestions?


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inputFile.open("TestScores.txt");
    
    while (!inputFile.eof())
    {
          inputFile >> id;
          inputFile >> score;
          if (score >= 0 && score <= 10)  
          {
               switch(score)
                    case

toum (353)
You can't compute the letter grade inside the loop because you need the average grade to compute them, and you don't have it yet.

What you need to do is store the ids and scores of all the students into arrays when you read the file.
Once you've computed the average grade, use the stored data to compute the letter grade for each student and put the 3 values (id, grade, letter grade) into the output file.
angrybeaver76 (21)
Ok I think I'm headed in the right direction. I just can't get the right data to save into the arrays for some reason. I was able to calculate the correct letter grade and output to new file, but I want to then read all 3 rows into arrays. When I try to run the menu options 2 and 3, the data it outputs is not right. :( why why why?

Sample "TestScores_Grades.txt" to read from:
10214 8 A-
19285 3 F
11753 5 B
11261 3 F
13893 -1 F
17611 7 A-
10587 3 F
15568 10 A



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

using namespace std;

int main()
{ 
    const char FILENAME[30] = "TestScores.txt";
      
    ifstream inFile;    
    int id, score, avg, s = 0, numofstudents = 0, totalgrade = 0;
    inFile.open(FILENAME);
    
    while (!inFile.eof())
    {
          inFile >> id;
          inFile >> score;
          if (score >= 0 && score <= 10)
          {
               totalgrade = totalgrade + score;
               numofstudents++;
               s = s + 1;
          }     
    }
    avg = totalgrade/numofstudents;  
    inFile.close();
    
    
    ifstream inFile2;
    ofstream outFile1;
    int idx;
    string grade;
    
    inFile2.open(FILENAME);
    outFile1.open("TestScores_Grades.txt");
    
    for(idx = 0; idx < s; idx++)
    {
         inFile2 >> id >> score;
         if (score == avg || score == avg +1)
              grade = "B";
         else if (score == avg + 2 || score == avg + 3)
              grade = "A-";
         else if (score == avg +4 || score == 10 )
              grade = "A";
         else if (score == avg - 1)
              grade = "C";
         else if (score <= (avg - 2))
              grade = "F";
         outFile1 << id << " " << score << " " << grade << endl;
    }
    inFile2.close();
    
    
    ifstream inFile3;
    int num, ids[idx], scores[idx];
    char grades[idx];
    
    inFile3.open("TestScores_Grades.txt");
    idx = 0;
    
    while (idx <= s && !inFile3.eof())
    {
         inFile3 >> ids[idx] >> scores[idx] >> grades[idx];
         idx++;
    }
    inFile3.close();
     
    do
    {
         cout << setw(30) << "QUIZ RESULTS MENU     " << endl;
         cout << setw(30) << "***************************" << endl << endl;
         cout << "   1. " << left << setw(30) << "List by Student ID" << endl;
         cout << "   2. " << setw(30) << "List by Student ID and Grades" << endl;
         cout << "   3. " << setw(30) << "List by Letter Grade" << endl;
         cout << "   4. " << setw(30) << "List by Numeric Grade" << endl;
         cout << "   5. " << setw(30) << "List Grades by Percentage" << endl << endl;
    
         cout << right << "Enter an option: " ;
         cin >> num;
         cout << endl;
         
         if (num == 1)
              cout << "This option sorts the student list by ID and writes it to a file.";
         if (num == 2)
         {
              //Read the new file and search for the target ID that the user enters.
              ifstream inFile4;
              inFile4.open("TestScores_Grades.txt");
              int target;
                           
              for(idx = 0; idx < s; idx++)
              {
                   cout << "Enter a student ID: ";
                   cin >> target;
                   if(ids[idx] = target)
                   {
                        cout << "Result: " << ids[idx] << " " << scores[idx] << " " << grades[idx] << endl; 
                   }
              }
         }
         
         else if (num == 3)
              //cout << "This option searches for students with a particular letter grade." << endl << endl;
         {
              //Read the file again and search for the target letter grade that the user enters.
              ifstream inFile4;
              inFile4.open("TestScores_Grades.txt");
              char targetGrade;
                           
              for(idx = 0; idx < s; idx++)
              {
                   cout << "Enter a letter grade: ";
                   cin >> targetGrade;
                   if(grades[idx] = targetGrade)
                        cout << "Result: " << ids[idx] << " " << scores[idx] << " " << grades[idx]; 
              }
         }
         
         else if (num == 4)
              cout << "This option sorts the list by numeric grade.";
         else if (num == 5)
              cout << "This option calculates the % of students with a particular grade.";    
         else if (num < 1 || num > 5)
              cout << "This is an invalid entry. Please rerun the program.";
         cout << endl << endl << endl;
    }
    while (num > 0 && num <= 5);

  
    system("PAUSE");
    return EXIT_SUCCESS;
}
Last edited on
toum (353)
Line 26, incrementation of "s" should be outside the "if".
Line 61, grades should be a string array, not a char array.
Lines 100 and 119, it should be "==" and not "=".
Lines 98-99 and 117-118, this code should be outside the loop.
angrybeaver76 (21)
thanks toum.

I'm getting this error now: no match for 'operator==' in 'grades[idx]==targetGrade'

I don't understand that one. Match for ==?
angrybeaver76 (21)
Nvm. I figured out the error. The error was for the variable 'targetGrade'. Hadn't changed it to string also.
angrybeaver76 (21)
Ok. I got menu options 2 and 3 to run. But when I run 5, it gives me results the first time, but I can't run 5 again. It crashes. What am I missing?


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

using namespace std;

int main()
{ 
    const char FILENAME[30] = "TestScores.txt";
      
    ifstream inFile;    
    int id, score, avg, s = 0, numofstudents = 0, totalgrade = 0;
    inFile.open(FILENAME);
    
    while (!inFile.eof())
    {
          inFile >> id;
          inFile >> score;
          if (score >= 0 && score <= 10)
          {
               totalgrade = totalgrade + score;
               numofstudents++;
               //s = s + 1;
          }
          s = s + 1;     
    }
    avg = totalgrade/numofstudents;  
    inFile.close();
    
    
    ifstream inFile2;
    ofstream outFile1;
    int idx;
    string grade;
    
    inFile2.open(FILENAME);
    outFile1.open("TestScores_Grades.txt");
    
    for(idx = 0; idx < s; idx++)
    {
         inFile2 >> id >> score;
         if (score == avg || score == avg +1)
              grade = "B";
         else if (score == avg + 2 || score == avg + 3)
              grade = "A-";
         else if (score == avg +4 || score == 10 )
              grade = "A";
         else if (score == avg - 1)
              grade = "C";
         else if (score <= (avg - 2))
              grade = "F";
         outFile1 << id << " " << score << " " << grade << endl;
    }
    inFile2.close();
    
    
    ifstream inFile3;
    int num, ids[idx], scores[idx];
    string grades[idx];
    
    inFile3.open("TestScores_Grades.txt");
    idx = 0;
    
    while (idx <= s && !inFile3.eof())
    {
         inFile3 >> ids[idx] >> scores[idx] >> grades[idx];
         idx++;
    }
    inFile3.close();
     
    do
    {
         cout << setw(30) << "QUIZ RESULTS MENU     " << endl;
         cout << setw(30) << "***************************" << endl << endl;
         cout << "   1. " << left << setw(30) << "List by Student ID" << endl;
         cout << "   2. " << setw(30) << "List by Student ID and Grades" << endl;
         cout << "   3. " << setw(30) << "List by Letter Grade" << endl;
         cout << "   4. " << setw(30) << "List by Numeric Grade" << endl;
         cout << "   5. " << setw(30) << "List Grades by Percentage" << endl << endl;
    
         cout << right << "Enter an option: " ;
         cin >> num;
         cout << endl;
         
         if (num == 1)
              cout << "This option sorts the student list by ID and writes it to a file.";
         if (num == 2)
         {
              ifstream inFile4;
              inFile4.open("TestScores_Grades.txt");
              int target;
              
              cout << "Enter a student ID: ";
              cin >> target;             
              for(idx = 0; idx < s; idx++)
              {
                   
                   inFile4 >> ids[idx] >> scores[idx] >> grades[idx];
                   if(ids[idx] == target)
                        cout << "Result: " << ids[idx] << " " << scores[idx] << " " << grades[idx] << endl; 
              }
              inFile4.close();
         }
         
         
         else if (num == 3)
         {
              ifstream inFile5;
              inFile5.open("TestScores_Grades.txt");
              string targetGrade;
              idx = 0; 
               
              while (idx <= s && !inFile5.eof())
              {
                   inFile5 >> ids[idx] >> scores[idx] >> grades[idx];
                   idx++;
              }
              cout << "Enter a grade: ";
              cin >> targetGrade;
              
              for(idx = 0; idx < s; idx++)
              {
                   if(grades[idx] == targetGrade)
                        cout << "Result: " << ids[idx] << " " << grades[idx] << endl;
              }
              
              inFile5.close();
         }
         else if (num == 4)
              cout << "This option sorts the list by numeric grade.";
         else if (num == 5)
         {
              ifstream inFile6;
              inFile6.open("TestScores_Grades.txt");
              string targetLetter;
              int p = 0, percent;
              
              while (idx <= s && !inFile6.eof())
              {
                   inFile6>> ids[idx] >> scores[idx] >> grades[idx];
                   idx++;
              }
              cout << "Enter the letter grade to calculate %: ";
              cin >> targetLetter;
              
              for (idx = 0; idx < s; idx++)
              {
                  if(grades[idx] == targetLetter)
                  {
                       p = p + 1;
                       percent = (p * 100)/s;                       
                  }                  
              } 
              
              cout << percent << " % of the students received a " << targetLetter << "." << endl;   
              inFile6.close();
         }    
         else if (num < 1 || num > 5)
              cout << "This is an invalid entry. Please rerun the program.";
         cout << endl << endl << endl;
    }
    while (num > 0 && num <= 5);

  
    system("PAUSE");
    return EXIT_SUCCESS;
}
toum (353)
I tried to run your program and there was no crash. What was your input ?

I noticed a small bug: you should reinitialize idx to 0 before doing the loop line 141.
angrybeaver76 (21)
It's not crashing for me now either. Hmm. I must've fixed something without knowing it.
I added the idx=0. Thanks!
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