How to Make a Java Program Quit When "Q" Is Inputted, Issue Is the Default Input Variable Is Double

Java: using a string to stop a while loop and it is consumed by following scanner input

One way to not pass the data from the sc scanner is to create a new Scanner Object. Lets call this one scan. This way when you refer to scan it won't know the sc scanners input from earlier.

In your if statement, you would refer to the scan scanner instead of the sc scanner.

The reason the data was being passed from the while loop to your if statement is because they both referred to the same object and when you called sc.hasNext() it read the last thing that you inputted into the console.

Java program that reads user input until 0 is entered, also makes a few calculations (evens/odds, average, etc.)

When reading the first numbers to populate large and small we only need to do that once. And without re-reading the numbers with in.nextInt() because that will eat up the next inputs that are entered, which was probably causing the not terminating at zero error.

while ((input = in.nextInt()) != 0) {

        if (counter == 0)
          small = large = input;

        if (input != 0)
            sum = input + sum;
            counter++;

        if (input > large)
            large = input;

        if (input < small)
            small = input;

        if (input % 2 == 0)
            even = even + 1;
        else
            odd = odd + 1;

        }

Java - Try/Catch NumberFormatException uses a former value?

I don't follow everything that you're saying, but these 2 lines (from within your catch block) look problematic...

spaceTestAndConvert(numInput.trim());
return Double.parseDouble(numInput.trim());

You are calling the spaceTestAndConvert function recursively, but throwing away the value. I don't understand why you would call it and not be interested in the value.

The second line is also a mess. You so carefully surround the first call to Double.parseDouble() with try/catch, but then you call it again within your catch block. If the second Double.parseDouble() generates a NumberFormatException, it will not be caught.

Q : Doing multiple loops and multiple if-statements and if-else-statements || RENTAL CAR CALCULATOR PROJECT

Here you go, i modified it a bit and put the whole thing in a while loop (while (cus != 0)) now it is working perfectly, try this code and do let me know if you have questions

package inter;

import java.util.InputMismatchException;
import java.util.Scanner;

public class Inter {

    public static void main(String []args){
    int count=0;
    int days;
    int cus = 10; // added
    double DailyFee=0, NontaxTotal, CarType, Total,FullTotal=0;
    boolean F1 = false, F2 = false;
    Scanner in=new Scanner(System.in);

    while (cus != 0) {

        while (true) {  
            System.out.println("If there are any customer press 1 else press 0");
        try {           
            cus=in.nextInt();
            if (cus == 0 || cus == 1) {  
                break;
            } else {
                System.out.println("Number must be either 1 or 0");
            }
        } catch (InputMismatchException ex) {
            System.out.println("Invalid entry");
            in.next();
        }
    }

        if(cus == 1) {           
            while(F1 == false) {
                F1 = true;
                count++;
                System.out.print("What vehical would you like to rent?\n");
                System.out.println("Enter 1 for an economy car");
                System.out.println("Enter 2 for a sedan car");
                System.out.println("Enter 3 for an SUV");
                try {
                    CarType = in.nextInt();
                    if (CarType <= 0 || CarType >= 4) {
                        System.out.print("Number must be 1-3\n");
                        System.out.println("Please enter 1 for an economy car");
                        System.out.println("Enter 2 for a sedan car");
                        System.out.println("Enter 3 for an SUV");
                        F1 = false;
                    } else {
                         if (CarType == 1) {
                             F1 = true;
                              DailyFee=31.76;
                    } else if(CarType == 2) {
                            F1 = true;
                              DailyFee=40.32;
                    } else if(CarType == 3) {
                            F1 = true;
                              DailyFee=47.56;
                    }
                    while (F2 == false) {
                        F2 = true;
                        try { 
                            System.out.print("Please enter the number of days rented. (Example; 3) : ");                           
                            days = in.nextInt();
                            if (days <= 0) {
                                System.out.println("Number of days must be more than zero");
                                F2 = false;
                            } else {
                                //days = in.nextInt();
                                double x=days;
                                NontaxTotal = (DailyFee * x);
                                Total = (NontaxTotal * 1.06);
                                FullTotal+=Total;
                            }
                        } catch(InputMismatchException ex) {
                            System.out.println("Answer must be a number");
                            F2 = false;
                            in.next();
                            }
                        }
                    F2 = false;
                    }
                } catch (InputMismatchException ex) {
                    F1 = false;
                    System.out.println("Answer must be a number"); 
                    in.next();
                }
            }
            F1 = false;
        }
    }
    System.out.println("Count of customers : " + count);
    System.out.printf("Total of the Day : $ %.2f", FullTotal);
    }
}

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