[tgcbraun]

Hello again my friends. I'm currently working on a project that involves coding a Student class and a tester Main class. One of the goals is to to display the student's information to the console and use a loop (while or do-while) to get project and quiz scores from the student object. I'm experiencing what seems to be an infinite loop when I use some getNextProjectIndex() and getNextQuizIndex() methods to find the indexes in which to add the aforementioned project and quiz scores.

Here's the Student class:

public class Student {
  
  private String lastName;
  private String firstName;
  private int studentId;
  private double[] projects;
  private double[] quizzes;
  
  public Student(String lastName, String firstName, int studentId){
	 
	  
	 this.lastName=lastName; 
	 this.firstName=firstName;
	 this.studentId=studentId;
	 
	 
	 projects = new double[] {-1.0, -1.0, -1.0, -1.0, -1.0, -1.0, -1.0, -1.0, -1.0, -1.0, 
		 -1.0,-1.0, -1.0, -1.0, -1.0,};
	 quizzes = new double [] {-1.0, -1.0, -1.0, -1.0, -1.0, -1.0, -1.0, -1.0, -1.0, -1.0};
			 		 
  }
  

public boolean setProjectScore(double newProjects, int projectNumber) {
		projects[projectNumber] = newProjects;
	  	if (projectNumber >= 0 || projectNumber <= 14)
			return true; else
			return false;
		
	  }
	   
  public boolean setQuizScore(double newQuizzes, int quizNumber) {
		 quizzes[quizNumber] = newQuizzes;
		 if (quizNumber >= 0 || quizNumber <= 9)
			return true; else
			return false;
	  }
	  
  public double getProjectScore(int projectNumber){
	  
	  if (projects[projectNumber] < 0 || projects[projectNumber] > 14)
		  	return -1.0; else
			  return projects[projectNumber];
  }
  
  public double getQuizScore(int quizNumber){
		  
		  if (quizzes[quizNumber] < 0 || quizzes[quizNumber] > 9)
			  	return -1.0; else
				  return quizzes[quizNumber];
  }
	  

  public int getNextProjectIndex(){
	  int nextProjectIndex=0;
	  while (nextProjectIndex <= 14)
		  if (projects[nextProjectIndex] == -1.0)
			  return nextProjectIndex; 
		  nextProjectIndex++;
		  
	  return -1;
	  
  }
  
  public int getNextQuizIndex(){
	  int nextQuizIndex=0;
	  while (nextQuizIndex <= 9)
		  if (projects[nextQuizIndex] == -1.0)
			  return nextQuizIndex; 
		  nextQuizIndex++;
		  
	  return -1;
	  
  }
  
  
	  
  public String getLastName() {
    return lastName;
  }
  public void setLastName(String lastName) {
    this.lastName = lastName;
  }
  public String getFirstName() {
    return firstName;
  }
  public void setFirstName(String firstName) {
    this.firstName = firstName;
  }
  public int getStudentId() {
    return studentId;
  }
  public void setStudentId(int studentId) {
    this.studentId = studentId;
  }
  
  

}

And here is the tester class:

public class Main {
	
	 public static void main(String[] args) {
		
		int i = 0; 
		int j = 0;
		 
		Student st = new Student("Braun", "Thiago", 1);
		
		System.out.println("Student Last Name is:" + " " + st.getLastName());
		System.out.println("Student First Name is:" + " " + st.getFirstName());
		System.out.println("Student ID is:" + " " + st.getStudentId());
		
		while (st.getProjectScore(st.getNextProjectIndex()) == -1.0){
				st.setProjectScore (70.0, (st.getNextProjectIndex()));
			}
		
		while (st.getQuizScore(st.getNextQuizIndex()) == -1.0){
			st.setQuizScore (85.0, (st.getNextQuizIndex()));
		}
			
		
		do {		
			System.out.println("Student Project Grades are:" + " " + st.getProjectScore(i));
			i++;			
		} while (i <= 14);
		
		
		do {		
			System.out.println("Student Quiz Grades are:" + " " + st.getQuizScore(j));
			j++;			
		} while (j <= 9);
		
		

I think there are some logical mistakes on both while methods that I haven't been able to figure out. When i run the Main class I get the results below and the applet enters on an infinite loop with nothing showing on the console. Only way to quit is to press the stop button.

Student Last Name is: Braun
Student First Name is: Thiago
Student ID is: 1

Thanks again for any input!

[salazar]

You need to have braces around your multiple statements. While loops consisting of no braces only executes the immediate statement that follows. This means that in the following, the nextProjectIndex will never get updated. Thus, you have an infinite loop.

while (nextProjectIndex <= 14)
		  if (projects[nextProjectIndex] == -1.0)
			  return nextProjectIndex; 
		  nextProjectIndex++;
		  

With braces:

while (nextProjectIndex <= 14)
{
		  if (projects[nextProjectIndex] == -1.0)
			  return nextProjectIndex; 
		  nextProjectIndex++;
}		  

[pbl]

also replace

       if (projectNumber >= 0 || projectNumber <= 14)
            return true; else
            return false;

by

       return (projectNumber >= 0 || projectNumber <= 14);

why complicating your life to return true or false ? Return the if that let you make the decision
But the more concise form prooves that your if is screwed anyway... it will always return true
any number is or >= 0 or <= 14

[tgcbraun]

Thank you guys very much.

Regarding the boolean, that´s one of the requirements of the project.

I made some changes and the code compiles fine, but the project and quiz grades are not being set correc.

Here´s the new Student and Main classes:

public class Student {
  
  private String lastName;
  private String firstName;
  private int studentId;
  private double[] projects;
  private double[] quizzes;
  
  public Student(String lastName, String firstName, int studentId){
   
    
   this.lastName=lastName; 
   this.firstName=firstName;
   this.studentId=studentId;
   
   
   projects = new double[] {-1.0, -1.0, -1.0, -1.0, -1.0, -1.0, -1.0, -1.0, -1.0, -1.0, 
     -1.0,-1.0, -1.0, -1.0, -1.0,};
   quizzes = new double [] {-1.0, -1.0, -1.0, -1.0, -1.0, -1.0, -1.0, -1.0, -1.0, -1.0};
           
  }
  

public boolean setProjectScore(double newProjects, int projectNumber) {
    projects[projectNumber] = newProjects;
      if (projectNumber >= 0 && projectNumber <= 14)
      return true; else
      return false;
    }
     
  public boolean setQuizScore(double newQuizzes, int quizNumber) {
     quizzes[quizNumber] = newQuizzes;
     if (quizNumber >= 0 && quizNumber <= 9)
      return true; else
      return false;
    }
    
  public double getProjectScore(int projectNumber){
    if (projects[projectNumber] < 0 || projects[projectNumber] > 14){
    	return -1.0;
    }   else {
    	  return projects[projectNumber];	
    }
      
  }
  
  public double getQuizScore(int quizNumber){
      if (quizzes[quizNumber] < 0 || quizzes[quizNumber] > 9){
    	  return -1.0;  
      } else
          return quizzes[quizNumber];
  }
    

  public int getNextProjectIndex(){
    int nextProjectIndex=0;
    while (nextProjectIndex <= 14) {
      if (projects[nextProjectIndex] == -1.0) 
        return nextProjectIndex; 
        nextProjectIndex++;
        
    }
    return -1;
    
  }
  
  public int getNextQuizIndex(){
    int nextQuizIndex=0;
    while (nextQuizIndex <= 9) {
      if (projects[nextQuizIndex] == -1.0)
        return nextQuizIndex; 
      nextQuizIndex++;
    } 
    return -1;
    
  }
  
  
    
  public String getLastName() {
    return lastName;
  }
  public void setLastName(String lastName) {
    this.lastName = lastName;
  }
  public String getFirstName() {
    return firstName;
  }
  public void setFirstName(String firstName) {
    this.firstName = firstName;
  }
  public int getStudentId() {
    return studentId;
  }
  public void setStudentId(int studentId) {
    this.studentId = studentId;
  }
  
  

}

public class Main {
	
	 public static void main(String[] args) {
		
		int i = 0; 
		int j = 0;
		int k = 0;
		int l = 0;
		 
		Student st = new Student("Braun", "Thiago", 1);
		
		System.out.println("Student Last Name is:" + " " + st.getLastName());
		System.out.println("Student First Name is:" + " " + st.getFirstName());
		System.out.println("Student ID is:" + " " + st.getStudentId());
			
		
		while (st.getProjectScore(st.getNextProjectIndex()) == -1.0 && i <=14){
			st.setProjectScore(70.0, 0);
			st.setProjectScore(70.0, 1);
			st.setProjectScore(70.0, 5);
			st.setProjectScore(70.0, 9);
			st.setProjectScore(70.0, 10);
			i++;
		}
		
		while (st.getQuizScore(st.getNextQuizIndex()) == -1.0 && j <=14){
			st.setQuizScore(70.0, 0);
			st.setQuizScore(70.0, 1);
			st.setQuizScore(70.0, 5);
			st.setQuizScore(70.0, 8);
			st.setQuizScore(70.0, 9);
			j++;
		}
	
		
	do {		
		System.out.println("Student Project Grades are:" + " " + st.getProjectScore(k));
		k++;
	} while (k <= 14);
	
	
	do {		
		System.out.println("Student Quiz Grades are:" + " " + st.getQuizScore(l));
		l++;
	} while (l <= 9);
	
		
	
		
		
	 }

}

I´m getting this result on the console:

Student Last Name is: Braun
Student First Name is: Thiago
Student ID is: 1
Student Project Grades are: -1.0
Student Project Grades are: -1.0
Student Project Grades are: -1.0
Student Project Grades are: -1.0
Student Project Grades are: -1.0
Student Project Grades are: -1.0
Student Project Grades are: -1.0
Student Project Grades are: -1.0
Student Project Grades are: -1.0
Student Project Grades are: -1.0
Student Project Grades are: -1.0
Student Project Grades are: -1.0
Student Project Grades are: -1.0
Student Project Grades are: -1.0
Student Project Grades are: -1.0
Student Quiz Grades are: -1.0
Student Quiz Grades are: -1.0
Student Quiz Grades are: -1.0
Student Quiz Grades are: -1.0
Student Quiz Grades are: -1.0
Student Quiz Grades are: -1.0
Student Quiz Grades are: -1.0
Student Quiz Grades are: -1.0
Student Quiz Grades are: -1.0
Student Quiz Grades are: -1.0

I was expecting some of the grades to be 70.0.

Thanks again!

[Mylo]

You are writing your get methods correctly:

if (projects[projectNumber] < 0 || projects[projectNumber] > 14)

Think about what this code is doing. What you need to be doing here is checking if a given index is valid, not the value stored in the array.
Such lines are to be changed to:

if (projectNumber < 0 || projectNumber > 14)

Also the lines like:

while (st.getProjectScore(st.getNextProjectIndex()) == -1.0 && i <=14){ // ... 

are not useful, you are doing the same thing 14 times. It only needs to be done once. You can remove the while construct, keeping the code inside it).

[tgcbraun]

That settles it! Thanks again for your kind attention, Mylo!

[Mylo]

No problem.

However, not to be mean, maybe it's just not your thing, but you don't seem to be understanding how to reason about such problems. I would suggest you try take on simpler projects without the aid of anyone else, and keep working at it until you get it right. This should help you reason with the problems you are given, and thus improve />

This post has been edited by Mylo: 30 August 2013 - 07:12 AM

[tgcbraun]

Thanks, Mylo! I will keep that in mind!