Thread: scanner questions

Thank you for your help in advance!

I'm new to programming and decided that I would make a basic console based ohms law calculator as practice. The way my code works currently is that you have to answer at least one value as "0" to find for that value... I've been trying to find a way to allow a user to skip past the desired value during the input phase, but have not come up with a way to do that and still use a "double" variable. Is there a way to allow the user to just press [Enter] to continue on to the next input value and still tell the program to find for that value?

Also, I've noticed that when I am finding for voltage and any other value I get a dummy voltage value (examples shown below)... anyone know where I went wrong? Can you point me in the right direction to research this issue?

Again, Thank you for your help.

Shaun



My Code:

package ohmslaw;
 
import java.util.Scanner;
 
public class Ohmslaw {
 
 
	public static void main(String[] args) {
 
		Scanner value = new Scanner (System.in);
 
		//declaring base variables for voltage (v), current (i), resistance (r), and power (p).
		double v;
		double i;
		double r;
		double p;
 
		//declaring v,i,r,p formula names.
		double voltage;
		double pivoltage;
		double prvoltage;
 
		double current;
		double pvcurrent;
		double prcurrent;
 
		double resistance;
		double vpresistance;
		double piresistance;
 
		double power;
		double irpower;
		double vrpower;
 
		//scanner inputs to initialize base variables for formulas.
		System.out.println("Voltage?");
		v = value.nextDouble();
 
		System.out.println("Current?");
		i = value.nextDouble();
 
		System.out.println("Resistance?");
		r = value.nextDouble();
 
		System.out.println("Power?");
		p = value.nextDouble();
 
		//v,i,r,p formulas.
		voltage = i*r;
		pivoltage = p/i;
		prvoltage = Math.pow(p*r, 0.5);
 
		current = v/r;
		pvcurrent = p/v;
		prcurrent = Math.pow(p/r, 0.5);
 
		resistance = v/i;
		vpresistance = (v*v)/p;
		piresistance = p/(i*i);
 
		power = v*i;
		irpower = (i*i)*r;
		vrpower = (v*v)/r;
 
 
		// print statements and formula logic.
 
		//voltage
		if(v==0){
			System.out.println("Voltage: " + voltage);
		}
		if(v==0 && r==0){
			System.out.println("Voltage: " + pivoltage);
		}
		if(v==0 && i==0){
			System.out.println("Voltage: " + prvoltage);
		}
 
		//current
		if(i==0){
			System.out.println("Current: " + current);
		}
		if(i==0 && r==0){
			System.out.println("Current: " + pvcurrent);
		}
		if(i==0 && v==0){
			System.out.println("Current: " + prcurrent);
		}
 
		//resistance
		if(r==0){
			System.out.println("Resistance: " + resistance);
		}  
		if(r==0 && i==0){
			System.out.println("Resistance: " + vpresistance);
		}
		if(r==0 && v==0){
			System.out.println("Resistance: " + piresistance);
		}
 
		//power
		if(p==0){
			System.out.println("Power: " + power);
		}
		if(p==0 && v==0){
			System.out.println("Power: " + irpower);
		}
		if(p==0 && i==0){
			System.out.println("Power: " + vrpower);
		}
 
	}
 
}

Example of double output (testing for voltage and resistance):

Voltage?
0
Current?
2.5
Resistance?
0
Power?
15
Voltage: 0.0
Voltage: 6.0
Resistance: 0.0
Resistance: 2.4

Thank you, after testing this out I think I need to do a bit more research on converting strings to a double using your Double.parseDouble(String) example.

@Silverknight: Welcome to the Forum! Please read this topic to learn how to post your code correctly along with other useful info for newcomers.

So, after making a few changes, (not sure if I'm actually using the Double.parseDouble(String) method correctly.) I'm left with the same issue... I think the issue now lies within my logic where I ask for 0 such as v2==0.

When I try to press [Enter] when there isn't a value given I get this error:

Exception in thread "main" java.lang.NumberFormatException: empty String
at sun.misc.FloatingDecimal.readJavaFormatString(Unkn own Source)
at java.lang.Double.parseDouble(Unknown Source)
at ohmslaw.Ohmslaw.main(Ohmslaw.java:44)

Here is what my code looks like now:

package ohmslaw;
 
import java.util.Scanner;
 
public class Ohmslaw {
 
 
	public static void main(String[] args) {
 
		Scanner value = new Scanner (System.in);
 
 
		//declaring base variables for voltage (v), current (i), resistance (r), and power (p).
 
		String v;
		String i;
		String r;
		String p;
 
		//declaring v,i,r,p formula names.
		double voltage;
		double pivoltage;
		double prvoltage;
 
		double current;
		double pvcurrent;
		double prcurrent;
 
		double resistance;
		double vpresistance;
		double piresistance;
 
		double power;
		double irpower;
		double vrpower;
 
		//scanner inputs to initialize base variables for formulas.
		System.out.println("Voltage?");
		v = value.nextLine();
		double v2 = Double.parseDouble(v);
 
		System.out.println("Current?");
		i = value.nextLine();
		double i2 = Double.parseDouble(i);
 
		System.out.println("Resistance?");
		r = value.nextLine();
		double r2 = Double.parseDouble(r);
 
		System.out.println("Power?");
		p = value.nextLine();
		double p2 = Double.parseDouble(p);
 
		//v,i,r,p formulas.
		voltage = i2*r2;
		pivoltage = p2/i2;
		prvoltage = Math.pow(p2*r2, 0.5);
 
		current = v2/r2;
		pvcurrent = p2/v2;
		prcurrent = Math.pow(p2/r2, 0.5);
 
		resistance = v2/i2;
		vpresistance = (v2*v2)/p2;
		piresistance = p2/(i2*i2);
 
		power = v2*i2;
		irpower = (i2*i2)*r2;
		vrpower = (v2*v2)/r2;
 
 
		// print statements and formula logic.
 
		//voltage
		if(v2==0){
			System.out.println("Voltage: " + voltage);
		}
		if(v2==0 && r2==0){
			System.out.println("Voltage: " + pivoltage);
		}
		if(v2==0 && i2==0){
			System.out.println("Voltage: " + prvoltage);
		}
 
		//current
		if(i2==0){
			System.out.println("Current: " + current);
		}
		if(i2==0 && r2==0){
			System.out.println("Current: " + pvcurrent);
		}
		if(i2==0 && v2==0){
			System.out.println("Current: " + prcurrent);
		}
 
		//resistance
		if(r2==0){
			System.out.println("Resistance: " + resistance);
		}  
		if(r2==0 && i2==0){
			System.out.println("Resistance: " + vpresistance);
		}
		if(r2==0 && v2==0){
			System.out.println("Resistance: " + piresistance);
		}
 
		//power
		if(p2==0){
			System.out.println("Power: " + power);
		}
		if(p2==0 && v2==0){
			System.out.println("Power: " + irpower);
		}
		if(p2==0 && i2==0){
			System.out.println("Power: " + vrpower);
		}
 
	}
 
}