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I am trying to calculate the average for a class from scores given using a data file that was given.

The formula I'm using is grade_Average = sum / i;

The data file that was given is :

Joe Johnson 89
Susie Caldwell 67
Matt Baker 100
Alex Anderson 87
Perry Dixon 55

The output I am getting is

Johnson,Joe B
Caldwell,Susie D
Baker,Matt A
Anderson,Alex B
Dixon,Perry F

Class average inf

I am not sure if I have the formula wrong or if the formula is in the wrong place.

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

using namespace std;

int main()

 // Variable declarations: 
 string fName[10];
 string lName[10];
 float grade_Average;
 string file;
 string name;
 int scores[10];
 float sum = 0;
 char grade;
 int i = 0;

 ifstream din;

 // Function body: 

 cout << "Enter the name of the file. " << endl;
 cin >> file;

 din.open(file.c_str());

 if (!din)
 
 cout << " Cannot open the input file. Please try again." << endl;
 return 0;
 

 cout << setw(10) << setfill(' ') << "Name" <<setw(20)<<setfill(' ')<< "Grade" << endl;

 while (!din.eof())
 

 din >> fName[i];
 din >> lName[i];
 din >> scores[i];

 sum = sum + scores[i];

 switch (static_cast<int> (scores[i]/10))
 
 case 0:
 case 1:
 case 2:
 case 3:
 case 4:
 case 5:
 grade = 'F';
 break;
 case 6:
 grade = 'D';
 break;
 case 7:
 grade = 'C';
 break;
 case 8:
 grade = 'B';
 break;
 case 9:
 grade = 'A';
 break;
 case 10:
 grade = 'A';
 break;
 default:
 cout << "Invalid score." << endl;

 i++;
 

 name = lName[i] + ',' + fName[i];
 cout << setw(10) << setfill(' ') << name << setw(20) << setfill(' ')<<(" ") << grade << endl;


 
 grade_Average = sum / i;
 cout << "Class average " << grade_Average << endl;

 din.close();

 return 0;

Your i++ is inside the default block. The i variable is most probably 0. Either you put i++ outside of the switch block or you put it before every break statement.

i++ is inside the switch block and in the default case. It will never be executed for the given input. Therefore throughout the run i will just be 0. Dividing by 0 gives you inf.

Your program will also fail if more than 10 entries are given (and the first issue is corrected). You should use std::vector<std::string>, std::vector<int> and push_back instead of the raw arrays of std::string and int, if these arrays are needed at all. (For just calculating the average, the individual entries don't really need to be saved.)