How do I calculate average of each subject

Question

How do I calculate the average of each subject and average of the total value of 3 subjects and average of percentage and print them below the table.

I tried to find the average by dividing each array with number of students variable "DB" but it gives error

"The operator / is undefined for the argument type(s) int, int[][]".

And is there any way that I can get a perfect table structure for the output.

I'm using \\t to create space between columns but they do not align properly.

package cube;
  import java.io.*;
import java.util.Scanner;
  public class ReportCard
  {
    BufferedReader br=new BufferedReader(new InputStreamReader(System.in));
    int DB[][],nos=0; 
    String S="";
    Scanner s = new Scanner(System.in);
    void Input()throws Exception
    {
      System.out.print("Enter The Number Of Students : ");
      nos=Integer.parseInt(br.readLine());
      DB=new int[nos+1][20];
      String arrayOfNames[] = new String[nos];
        for (int i = 0; i < arrayOfNames.length; i++) {
            System.out.print("Enter the name of student:");
                arrayOfNames[i] = s.nextLine();


        System.out.print("\nEnter "+arrayOfNames[i]+"'s English   Score : ");
        DB[i][0]=Integer.parseInt(br.readLine());
        System.out.print("Enter "+arrayOfNames[i]+"'s Science Score : ");
        DB[i][1]=Integer.parseInt(br.readLine());
        System.out.print("Enter "+arrayOfNames[i]+"'s Maths  Score : ");
        DB[i][2]=Integer.parseInt(br.readLine());
        DB[i][3]=(int)(DB[i][0]+DB[i][1]+DB[i][2]);

        DB[i][4]=((int)((DB[i][3])*100)/300);

        DB[i][5]=(int)(DB[i][0])/DB;

        Padd("Average\t",DB[i][5]);

         if ((DB[i][0])< 50 | (DB[i][1])< 50 | (DB[i][2]) < 50) {

            System.out.print("Fail");
           }
        else {
            System.out.print("Pass");
        }
        }




      System.out.println("\n\n\nStudent Name.  English     Science  \t Maths    Total   Percentage     Pass or Fail \n");
      for(int i=0;i<nos;i++)
      {
          System.out.print(""+arrayOfNames[i]+"\t\t");Padd("English  \t ",DB[i][0]);Padd("Science  \t ",DB[i][1]);
        Padd("Maths  \t ",DB[i][2]);Padd("Total \t",DB[i][3]);Padd("Percentage\t",DB[i][4]);

if ((DB[i][0])< 50 | (DB[i][1])< 50 | (DB[i][2]) < 50) {

            System.out.print("\t\tFail");
           }
        else {
            System.out.print("\t\tPass");
        }

        System.out.println(S);

        S="";
      }

    }
    void Padd(String S,int n)
    {
      int N=n,Pad=0,size=S.length();
      while(n!=0)
      {
        n/=10;
        Pad++;
      }
      System.out.print("    "+N);
      for(int i=0;i<size-Pad-4;i++)
        System.out.print(" ");
          }


    public static void main(String args[])throws Exception
    {
      ReportCard obj=new ReportCard();
      obj.Input();

    }
  }

Answer 1

Your problem is in this section of code

DB[i][5]=(int)(DB[i][0])/DB;
Padd("Average\t",DB[i][5]);
if ((DB[i][0])< 50 | (DB[i][1])< 50 | (DB[i][2]) < 50) {
  System.out.print("Fail");
}
else {
  System.out.print("Pass");
}

From what I can understand from your code index 5 is not needed. You already stored the average in array index 4 (DB[i][4]).

Either way the division is illegal. An int cannot be divided by an array. Perhaps you mean the length of DB (DB.length)

Answer 2

You are getting this error as you are doing arithmetic operations on the array object itself.

Array in java is a data structure to hold sequential collection of values/objects. You can do arithmetic operations on elements of the array by accessing them using the index.

Like below: int result = array[i][0] / 3;

But in your code you are passing entire array as an operand in the expression.

DB[i][5]=(int)(DB[i][0])/DB;

Above line of code is causing the issue. Instead of providing any entire DB array, provide it's corresponding index according to your requirement

I hope this answers your question