How do I implement asking the user if they want to run my java program again?

Question

I tried multiple methods and I still can't figure out how to make it so that my code asks the user if they want to run it again in java. This is for my college project due in two days.

I've tried a couple of do-while statements but it still doesn't work.

public class Project_2_1
{
   public static void main(String args[])
   {

     System.out.println("My project");

     System.out.println("Project_2 Problem_1\n");

     System.out.println("This program computes both roots of a quadratic equation,\n");
     System.out.println("Given the coefficients A,B, and C.\n");

      double secondRoot = 0, firstRoot = 0;
      Scanner sc = new Scanner(System.in);


      System.out.println("Enter the value of a ::");
      double a = sc.nextDouble();

      System.out.println("Enter the value of b ::");
      double b = sc.nextDouble();

      System.out.println("Enter the value of c ::");
      double c = sc.nextDouble();

      double determinant = (b*b)-(4*a*c);
      double sqrt = Math.sqrt(determinant);

      if(determinant>0)
      {
         firstRoot = (-b + sqrt)/(2*a);
         secondRoot = (-b - sqrt)/(2*a);
         System.out.println("Roots are :: "+ firstRoot +" and "+secondRoot);
      }else if(determinant == 0){
         System.out.println("Root is :: "+(-b + sqrt)/(2*a));

      }
    }

  }

Answer 1

So what you are looking for is the idea of a loop. There are three basic types of loops.

• A for loop. Commonly used to loop over a Collection, such as an ArrayList, Map, or Array. Syntax for this typically looks like:

  for (int i = 0; i < someSize; i++){ }
  

• A while loop. Typically used for loops when you do not know when they will exit. Syntax for a simple loop looks like this:

  boolean condition = true;
  while(condition) {  
      //Code that will make condition false in a certain scenario
  }
  

• A do while loop. This is a variant on a while loop when you are certain you want the block of code to run at least one time. A sample of this looks like:

  boolean condition = //can be set default to true or false, whichever fits better
  do{
  //Any code you want to execute
  //Your code that will determine if the condition is true or false
  
  } while (condition);
  

A do while loop is what fits your program the best, because you want to run it AT least a single time, every time the program is ran. So all you need to do is stick it inside of a loop and create your condition.

I got you started with the skeleton below:

    Scanner sc = new Scanner(System.in);
    int choice = 0;
    do{
        System.out.println("Hi, I am being repeated until you tell me stop!"); //Replace this with your code

        System.out.println("Enter 1 to run the program again, 0 to exit.");
        choice = sc.nextInt();

    }while (choice == 1);
    sc.close();

Answer 2

You could add something like into the main method, but copy all the content into this while, now your code will run until you kill the process.

  while(true){
  System.out.println("My project");

     System.out.println("Project_2 Problem_1\n");

     System.out.println("This program computes both roots of a quadratic equation,\n");
     System.out.println("Given the coefficients A,B, and C.\n");

      double secondRoot = 0, firstRoot = 0;
      Scanner sc = new Scanner(System.in);


      System.out.println("Enter the value of a ::");
      double a = sc.nextDouble();

      System.out.println("Enter the value of b ::");
      double b = sc.nextDouble();

      System.out.println("Enter the value of c ::");
      double c = sc.nextDouble();

      double determinant = (b*b)-(4*a*c);
      double sqrt = Math.sqrt(determinant);

      if(determinant>0)
      {
         firstRoot = (-b + sqrt)/(2*a);
         secondRoot = (-b - sqrt)/(2*a);
         System.out.println("Roots are :: "+ firstRoot +" and "+secondRoot);
      }else if(determinant == 0){
         System.out.println("Root is :: "+(-b + sqrt)/(2*a));

      }

    }

I'm not giving you the whole answer, but notice that if you modify this code asking some input from your user, you could set a different condition for the while loop and start and stop your program depending on user input.

Answer 3

Put all your code into a separate method then prompt the user and ask if user wants to run the program again. This repetitive calling of the same method is called recursion.

Lets call the method run.

public static void run() {
    ** put all the code from your main method here **

     Scanner s = new Scanner(System.in);
     System.out.println("Would you like to run program again? (Y for yes, N for no)");
     String decision = s.next();
     if(decision.equals("Y")) {
         run();
     } else {
         System.out.println("Finished");
     }
}

public static void main(String args[]) {
   run();
}