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Thread: Need Help with Operators/ logic

  1. #1
    Junior Member codekiller's Avatar
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    Default Need Help with Operators/ logic

    Okay, I'm very, very new to java. I'm in an intro to computer science class and we got out first assignment to write a program. its from "An Into to Object Oriented Programming with java" by C. Thomas Wu.

    all we have to do is create a program that calculate body mass index using the formula Bmi=Weight/(Height/100)^2 where weight is in kg and height is in cm.

    Here is my code:
     
    import javax.swing.*;
     
    class Bmi
    {
    	public static void main(String[] args)
    	{
    		//*****
    		// Declarations:
    		//*****
     
    		final double NUM1=100.0;	//The constant 100 in the formula
    		String weightin;				//weight input
    		String heightin;				//height input
    		String description;			//if the output bmi is normal
    		int weightp;					//weight primitive
    		int heightp;					//height primitive
    		double denom;					//height/NUM1
    		double denommod;				//(height/NUM1)(height/NUM1)
    		double bmi;						//final value-bmi
     
    		heightin=JOptionPane.showInputDialog(null,"Please Enter your weight:\n (Kilograms)"); 						 //get weight
    		weightin=JOptionPane.showInputDialog(null,"Thanks you. Now, Please enter your Height:\n (centimeters)"); //get height
     
    		weightp=Integer.parseInt(weightin);		// convert height and weight to primitive values
    		heightp=Integer.parseInt(heightin);
     
    		denom=(heightp/NUM1);			//calulations
    		denommod=(denom*denom);
    		bmi=(weightp/denommod);
     
    		if(bmi<=18.5);							//Understanding what the value means
    			description="underweight";
    		if((bmi>18.5)&(bmi<=25));
    			description="normal";
    		if((bmi>25)&(bmi<=30));
    			description="overweight";
    		if(bmi>30);
    			description="obese";
     
    		JOptionPane.showMessageDialog(null,"Your Body mass index is:" +bmi+ " \n This is considered " +description+".");
    	}
    }

    I think the problem is in the middle chunk there with the operators labelled "calculations"
    but it could be my data types?
    my professor (who i think to be completely incompetent) told us to use these test parameters to start:
    50 kg and 160 cm

    i keep getting 640 with this program but the correct answer is roughly 19.5

    if you could point out any convention errors, too, that would be great!
    thanks!


  2. #2
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    Default Re: Need Help with Operators/ logic

    I don't notice anything wrong. Your formula seems correct and there is nothing noticeably wrong syntactically.

  3. #3
    Super Moderator Norm's Avatar
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    Default Re: Need Help with Operators/ logic

    Try debugging your code by printing out the values of all the variables used in your calculations to see where your formulas are going wrong.

  4. #4
    Junior Member codekiller's Avatar
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    Default Re: Need Help with Operators/ logic

    Mahaa! i found it. if you look at the code, i had prompted for weight and stored it in height and vice versa.

    but now theres another problem!

    heres the new code:
    import javax.swing.*;
     
    class Bmi
    {
    	public static void main(String[] args)
    	{
    		//*****
    		// Declarations:
    		//*****
     
    		final double NUM1=100.0;	//The constant 100 in the formula
    		String weightin;				//weight input
    		String heightin;				//height input
    		String description;			//if the output bmi is normal
    		int weightp;					//weight primitive
    		int heightp;					//height primitive
    		double denom;					//height/NUM1
    		double denommod;				//(height/NUM1)(height/NUM1)
    		double bmi;						//final value-bmi
     
    		heightin=JOptionPane.showInputDialog(null,"Please Enter your Height:\n (Centimeters)"); 						 //get weight
    		weightin=JOptionPane.showInputDialog(null,"Thanks you. Now, Please enter your Weight:\n (Kilograms)"); //get height
     
    		weightp=Integer.parseInt(weightin);		// convert height and weight to primitive values
    		heightp=Integer.parseInt(heightin);
     
    		denom=(heightp/NUM1);			//calulations
    		denommod=(denom*denom);
    		bmi=(weightp/denommod);
     
    		if(bmi<=18.5);							//Understanding what the value means
    			description="underweight";
    		if((bmi>18.5)&(bmi<=25));
    			description="normal";
    		if((bmi>25)&(bmi<=30));
    			description="overweight";
    		if(bmi>30);
    			description="obese";
     
    		JOptionPane.showMessageDialog(null,"Your Body mass index is:" +bmi+ " \n This is considered " +description+".");
    	}
    }

    This time the problem is that it always tells me the bmi is obese. obviously an issue with the boolean logic. this isnt required for the project but i wanted to experiment. also, how do i keep the program from delivering the bmi with more than just a few decimal places?
    Thanks!
    Java is like a good woman:
    Shes fun to play with,
    She looks nice,
    She always tells the truth,
    And She even takes out the GARBAGE.

  5. #5
    Super Moderator Norm's Avatar
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    Default Re: Need Help with Operators/ logic

    how do i keep the program from delivering the bmi with more than just a few decimal places
    Look at the DecimalFormat class for formatting doubles to desired formats.

  6. #6
    Junior Member codekiller's Avatar
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    Default Re: Need Help with Operators/ logic

    okay, all fixed. thanks for the help!
    Java is like a good woman:
    Shes fun to play with,
    She looks nice,
    She always tells the truth,
    And She even takes out the GARBAGE.

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