new to java.. code question

[mziel]

hey guys.. i'm new to java (college course).. and i'm currently writing a grading program for a class.
basically all you do is input 3 quiz grades, two midterm grades, and one final grade. It's weighted.. 25% for quizzes, 35% for midterms, and 40% for the final.
i have the code written out completely but it's coming up with some errors. if i input all perfect scores (three 10's, two 100's, and one 100), the result is "1.0, A". Fair enough.. but if I put in anything else, it comes up with something like ".54, Fail", or another number (depending on what i put in). two questions... how might I convert the decimals (1.0 for example) into the actually percentage? (i.e. 1.0 would be 100)? Also, how might I actually get it to work correctly??
any tips?? i'm not looking for someone to write it for me correctly... just some guidance..
Here's my code:

import java.util.Scanner;

public class Proj1 
{
	public static void main(String[] args)
	{
	Scanner keyboard = new Scanner(System.in);
	
	System.out.println("Enter three quiz grades: ");
	int quizGrade1 = keyboard.nextInt();
	int quizGrade2 = keyboard.nextInt();
	int quizGrade3 = keyboard.nextInt();
	
	double totalQuizGrade = (quizGrade1 + quizGrade2 + quizGrade3);
	totalQuizGrade = totalQuizGrade / 30;
	totalQuizGrade = totalQuizGrade * .25;
	
	System.out.println("Enter two midterm grades: ");
	int midtermGrade1 = keyboard.nextInt();
	int midtermGrade2 = keyboard.nextInt();
	
	double totalMidtermGrade = (midtermGrade1 + midtermGrade2);
	totalMidtermGrade = totalMidtermGrade / 200;
	totalMidtermGrade = totalMidtermGrade * .35;
	
	System.out.println("Enter final exam grade: ");
	int finalExam = keyboard.nextInt();
	double totalFinalCalc = finalExam / 100;
	totalFinalCalc = totalFinalCalc * .40;
	
	double totalGrade = (totalQuizGrade + totalMidtermGrade + totalFinalCalc);
	int totalGrade1 = (int)totalGrade / 10;
	switch(totalGrade1)
	{
	case 10: case 9:
		System.out.println(totalGrade + ", A");
		break;
	case 8:
		System.out.println(totalGrade + ", B");
		break;
	case 7:
		System.out.println(totalGrade + ", C");
		break;
	case 6:
		System.out.println(totalGrade + ", C");
		break;
		default:
			System.out.println(totalGrade + ", Fail");
		break;
		
	}
	}
}

_____________thanks for any help!!
mziel

[Belisarius]

Well, as far as converting decimal to a percentage, simply multiply by 100. After all, .54 is 54 percent of 1, whereas 1 would be 100 percent of 1. It would still be a "decimal", in that you would end up with a number like "100.0", but I assume that's acceptable.

Also, part of your problem very well might be that you're 'casting' between doubles and integers. Being that you're new to Java, you might not know what a 'cast' is. Here is an example:

double foo = 5.75;
int bar = (int)foo;

Now, the problem with this is that I'm attempting to 'cast', or change the 'type' from a 'double' (or as you would understand it, decimal) to an 'int' (which is short for 'integer'). An integer is a whole number, that is 1, 2, 3, 4, 5, etc but *not* 1.1, 2.4, 5,1. By 'casting' from a 'double' to an 'int', I loose the decimal portion. No rounding takes place, the end is just dropped. So 5.75 becomes simply 5.

I think you can see how that could screw up your math. Be sure to keep everything the same. I'd suggest that you use a System.out.println() to see if 'totalGrade1' is what you expect it to be.

[mziel]

Hey Belisarius, thanks so much for your reply! I do have some background in programming (C++ class last semester).. so I got what you were saying haha. Although.. I did get things to work.. somewhat. Here is the input/output(I'm using eclipse):

Enter three quiz grades:
10 9 8
Enter two midterm grades:
100 70
Enter final exam grade:
100

0.9225, Fail

How would I get the output to be simply 92? and how would i be able to get it to be read into the switch statement as 10(for 100 percent) or 9, 8, etc.? I'm using switch instead of an if elseif because my prof. said the switch is better practice.. but I can't figure out how to compare the numbers to get the grades without being redundant, etc. Anything?

[Belisarius]

In this case, your professor is right about best practice and switches.

The simplest solution, since the way you store the grade is between 0 and 1, would be to simply multiply it by 10 before it goes into the switch statement. Then convert it to an 'int', which will eliminate any decimals.

[toe_cutter]

Originally Posted by Belisarius

In this case, your professor is right about best practice and switches.

Is it best practice because it looks nicer?

[Belisarius]

Well, presentation is certainly a factor - you want the code to flow naturally and when looking at a series of conditions, a switch statement is easier to understand. But it also is a performance gain, as the compiler can optimize a switch in a different manner than an "if" statement. When one has a number of integers for which a different action must be taken, you will generally see a performance gain by using a switch as opposed to an "if" statement. Generally the performance gain is minimal, as the majority of the time you'd use it the scope versus processor power makes the computation time almost irrelevant. But, if you have to do it an obscene number of times, it's probably better.

So in summary, yes there is a technical reason to do it, but the layout/clear flow of logic is the main reason. In more complex designs, frequently it's advantagous to replace a switch with a polymorphic design, but when simply comparing a set list a switch is the best way to go.

[toe_cutter]

Originally Posted by Belisarius

Well, presentation is certainly a factor - you want the code to flow naturally and when looking at a series of conditions, a switch statement is easier to understand. But it also is a performance gain, as the compiler can optimize a switch in a different manner than an "if" statement. When one has a number of integers for which a different action must be taken, you will generally see a performance gain by using a switch as opposed to an "if" statement. Generally the performance gain is minimal, as the majority of the time you'd use it the scope versus processor power makes the computation time almost irrelevant. But, if you have to do it an obscene number of times, it's probably better.

So in summary, yes there is a technical reason to do it, but the layout/clear flow of logic is the main reason. In more complex designs, frequently it's advantagous to replace a switch with a polymorphic design, but when simply comparing a set list a switch is the best way to go.

Ya, I asked because I am a C guy and I believe (not possitive) in C when you compile a switch statement and an if statement that do the same thing they will look identical in assembly. So the only benefit in C is that I think switch statements look nicer.

Thanks for the info.