Got another problem PLEASE HELP

Question

this is what i have....it reads test scores then prints the min max and average.....also categorizes the grades into a, b, c, d, f......and gives what percent of the test scores are these grades....so far it doesn't read the right amount of grades....percents remain at 0...and the max and min is wrong...any ideas?
public class ReadGrades5
public static double next;
public static void main(String[] args)
int numberOfA, numberOfB, numberOfC, numberOfD, numberOfF;
int numberOfStudents;
double sum, max, min;
char answer;
do
System.out.println("Please enter the list of Exam Scores.");
System.out.println("Enter a negative number to exit.");
max = 0;
min = 0;
sum = 0;
numberOfStudents = 0;
numberOfA = 0;
numberOfB = 0;
numberOfC = 0;
numberOfD = 0;
numberOfF = 0;
next = SavitchIn.readLineDouble();
while (next>=0)
if(next < min)
min = next;
if(next > max)
max = next;
if (min <= 0)
min = 100;
sum = sum + next;
numberOfStudents++;
next = SavitchIn.readLineDouble();
if (next>=90)
numberOfA++;
numberOfStudents++;
else if (next>=80)
numberOfB++;
numberOfStudents++;
else if (next>=70)
numberOfC++;
numberOfStudents++;
else if (next>=60)
numberOfD++;
numberOfStudents++;
else if (next<60)
numberOfF++;
numberOfStudents++;
next = SavitchIn.readLineDouble();
if (next < 0)
System.out.println("Total number of grades = " +numberOfStudents);
System.out.println("Number of A's = " + numberOfA + " " +(numberOfA/(int)numberOfStudents)*100 + "%");
System.out.println("Number of B's = " + numberOfB+ " " +(numberOfB/(int)numberOfStudents)*100 + "%");
System.out.println("Number of C's = " + numberOfC+ " " +(numberOfC/(int)numberOfStudents)*100+ "%");
System.out.println("Number of D's = " + numberOfD+ " " +(numberOfD/(int)numberOfStudents)*100+ "%");
System.out.println("Number of F's = " + numberOfF+ " " +(numberOfF/(int)numberOfStudents)*100+ "%");
System.out.println("The average score is " + (sum/numberOfStudents));
System.out.println("The highest score is " + max);
System.out.println("The lowest score is " + min);
else
System.out.println("Please enter the grades.");
System.out.println("");
System.out.println("Do you want to input more scores?");
System.out.println("Enter y for yes or n for no.");
answer = SavitchIn.readLineNonwhiteChar();
}while ((answer == 'y') || (answer == 'Y'));
}

Answer 1

Upon request from someone besides ^^you^^ (don't mean to offend you by not following what you said)
this is what i have
public class ReadGrades5
public static double next;
public static void main(String[] args)
int numberOfA, numberOfB, numberOfC, numberOfD, numberOfF;
int numberOfStudents;
int studentsForPercent;
double sum, max, min;
char answer;
do
System.out.println("Please enter the list of Exam Scores.");
System.out.println("Enter a negative number to exit.");
max = 0;
min = 0;
sum = 0;
numberOfStudents = 0;
studentsForPercent = 0;
numberOfA = 0;
numberOfB = 0;
numberOfC = 0;
numberOfD = 0;
numberOfF = 0;
next = SavitchIn.readLineDouble();
while (next>=0)
if(next < min)
min = next;
if(next > max)
max = next;
sum = sum + next;
numberOfStudents++;
next = SavitchIn.readLineDouble();
while (next>=0)
if(next !< 0)
sum = sum + next;
if (next>=90)
numberOfA++;
studentsForPercent++;
else if (next>=80)
numberOfB++;
studentsForPercent++;
else if (next>=70)
numberOfC++;
studentsForPercent++;
else if (next>=60)
numberOfD++;
studentsForPercent++;
else if (next<60)
numberOfF++;
studentsForPercent++;
next = SavitchIn.readLineDouble();
if (next < 0)
System.out.println("Total number of grades = " +numberOfStudents);
System.out.println("Number of A's = " + numberOfA + " " +(numberOfA/(double)studentsForPercent)*100 + "%");
System.out.println("Number of B's = " + numberOfB+ " " +(numberOfB/(double)studentsForPercent)*100 + "%");
System.out.println("Number of C's = " + numberOfC+ " " +(numberOfC/(double)studentsForPercent)*100+ "%");
System.out.println("Number of D's = " + numberOfD+ " " +(numberOfD/(double)studentsForPercent)*100+ "%");
System.out.println("Number of F's = " + numberOfF+ " " +(numberOfF/(double)studentsForPercent)*100+ "%");
System.out.println("The average score is " + (sum/numberOfStudents));
System.out.println("The highest score is " + max);
System.out.println("The lowest score is " + min);
else
System.out.println("Please enter the grades.");
System.out.println("");
System.out.println("Do you want to input more scores?");
System.out.println("Enter y for yes or n for no.");
answer = SavitchIn.readLineNonwhiteChar();
}while ((answer == 'y') || (answer == 'Y'));