Question

Having some coding issues.

I can't seem to figure out why my calculation is coming out incorrect for the fourth column. For example, mathematically speaking the first row, columns 1-3:

​19, 68, 10. Using the specific equation: finalGrade = e1*.30 + e2*.30 + f*.40. I should get 30.1 in the 4th column but I get otherwise. See provided screenshot.

Please explain what I am doing wrong?

/* Program info:
Fill dd array 30 and 3 of grades
Double course[30][3](rows = students; col = exams)
1 - Fill it randomly
2 - fill a one dim array of 30 grades / students e1 * .30 + e2 * .30 + f * .40
*/

#include <iostream>
#include <cstdlib>
#include <cmath>
#include <iomanip>
#include <ctime>
using namespace std;

int main()
{

double course[30][3];
int i, j; // i - (row) = students, j - (col) = exams


srand(time(0));

for (i = 0; i < 30; i++)
{
  for (j = 0; j < 3; j++)
  {
   course[i][j] = (rand() %100)+1;
  }
}

for (i = 0; i < 30; i++)
{
  double finalGrade = 0.0;
  for (j = 0; j < 3; j++)
  {
   cout << setw(4) << course[j][i] << ' '; // display table
   //finalGrade+= course[j];
   finalGrade = (course[i][j] * (.30)) + (course[i][j] * (.30)) + (course[i][j] * (.40)); //to multiply the first column by .30,
                      //multiply the second column by .30,
                      //and multiply the 3rd column by .40
                      //and sum them all together.
  }

  cout << setw(4) << finalGrade; // displays the final grade each student received for course on the 4th column.
  
  cout << endl;
}

system("pause");
return 0;
}

19 68 10 39 22 47 56 8 39 8 85 85 68 10 21 63 47 56 59 42 8 85 63 76 10 21 91 91 56 59 25 56 85 63 42 2Θ 21 91 88 57 59 25 27 3 63 42 76 47 91 88 78 59 25 27 51 75 42 76 91 86 88 78 84 87 27 51 83 26 76 91 56 44 78 844 48 51 83 89 87 91 56 20 1 84 4 29 34 3 94 56 20 57 26 4 29 84 42 89 3 51 66 20 57 3 8 29 84 58 41 3 51 35 58 3 47 31 83 89 57

Answer 1

1. Problem is with using inner for loop.

2. In the current code, final grade is been calculating three times once for each j value.

3. Final grade has to be calculated using three columns (0, 1, 2)

_______________________________________________________________________________________________

Updated Code:

// studentGradesCode.cpp : Defines the entry point for the console application.
//

#include "stdafx.h"

#include <iostream>
#include <cstdlib>
#include <cmath>
#include <iomanip>
#include <ctime>

using namespace std;

int main()
{

   double course[30][3];
   int i, j; // i - (row) = students, j - (col) = exams


   srand(time(0));

   for (i = 0; i < 30; i++)
   {
       for (j = 0; j < 3; j++)
       {
           course[i][j] = (rand() %100)+1;
       }
   }

  
   for (i = 0; i < 30; i++)
   {
       double finalGrade = 0.0;
      
       //to multiply the first column by .30,
        //multiply the second column by .30,
        //and multiply the 3rd column by .40
        //and sum them all together.

       /*
           - Removed Inner for loop
           - Specify column number directly
           - Print all the values  
       */

       //Calculating final grade
       finalGrade = (course[i][0] * (.30)) + (course[i][1] * (.30)) + (course[i][2] * (.40));
      
       //Printing result
       cout << setw(4) << course[i][0] << setw(4) << course[i][1] << setw(4) << course[i][2] << "   " << setw(4) << finalGrade; // displays the final grade each student received for course on the 4th column.

       cout << endl;
   }

   system("pause");
   return 0;
}

______________________________________________________________________________________________

Sample Output:

cluserslsaibabu\documentslvisual studio 20101Proje 61 55 42 51.6 22 22 57 35 4 10 15.7 83 89 42 68.4 36 614 19 46 54 41.1 40 79 92 719.7 85 83 68 77.6 49 92 49 887.5 38 25 63 29.2 12 80 20 35.6 73 34 63 394.7 36 46 5847.8 72 91 90 84.9 58 66 14 42.8 80 20 94 67.6 37 26 34 32.5 54 46 84 63.6 26 81 20 40.1 20 13 40 25.9 23 10 2821.1 22 32 8148.6 5 18 43 2.1 44 5 98 53.9 99 17 13 63 43 43 12 88 20 83 7961 84 12 93 5 63 45 38.4 Press any key to continue .. .