成绩计算器程序

Question

I'm totally stuck on this project, in which a user is supposed to enter number of students in a class, and number of exams taken. Then they enter each student's name, and then the exam scores for that student on a single line separated by blank spaces. The program calculates each student's average and the corresponding letter grade.

This is what I have so far:

public class proj2 {

 public static void main(String[] args) {
 Scanner s = new Scanner(System.in);

  System.out.println("Welcome to Gradecalculator!");

  System.out.println("Please enter the number of students:");
  int students = s.nextInt();

  System.out.println("Please enter the number of exams:");
  int exams = s.nextInt();

  int i = 0;
  int studentnumber = 1;

  int sum = 0;  
  while (i < students) {

    double average = sum/exams;

    System.out.println("Enter student " + studentnumber++ + "'s name :");
    String studentname = s.next();

    System.out.println("Enter exam scores :");

    for (; i < exams; i++) {    
     int n = s.nextInt();
     sum+=n;

     if (n < 0) {
     System.out.println("Invalid exam scores, reenter: ");      
     }
  }
  if (average <= 100 && average >= 90) {
       System.out.println("Letter grade: A");
       System.out.println(studentname + " gets 4 stars! ****");
      } if (average <= 89 && average >= 80) {
       System.out.println("Letter grade: B");
       System.out.println(studentname + " gets 3 stars! ***");
      } if (average <= 79 && average >= 70) {
       System.out.println("Letter grade: C");
       System.out.println(studentname + " gets 2 stars! **");
      } if (average <= 69 && average >= 60) {
       System.out.println("Letter grade: D");
       System.out.println(studentname + " gets 1 star! *");
      } if (average <= 59) {
       System.out.println("Letter grade: F");
       System.out.println(studentname + " gets 0 stars!");
      }
}
 }
 }

This is the output I get as of now:

Welcome to Gradecalculator!

Please enter the number of students: 3 Please enter the number of exams: 3 Enter student 1's name : sam Enter exam scores : 80 80 80 Letter grade: F sam gets 0 stars!

Obviously three 80's should be a B first of all, so I'm obviously not calculating the average properly, but I can't figure out why.

Answer 1

Your conditions should look like this :

if (average <= 100 && average >=90)

not like this :

if (average <= 100 & average >=90)

You want to use logical AND and not bitwise AND.

Another problem is that you reset sum to 0 in each iteration, so you are not actually accumulating the sum.

Finally, the calculation of the average and all the conditions should be outside the for loop, since you want to read all the inputs before calculating the average.

Answer 2

You have done a small mistake here.

if (average <= 100 & average >= 90)

I think you're trying to use logical AND use double & like this.

if (average <= 100 && average >= 90)

and you need to change your code little more. You need to declare sum outside for loop because every time its getting reset to 0 .

int sum = 0;
for (; i < exams; i++) {  
   int n = s.nextInt();
   sum+=n;
}
double average = sum/exams;