在递归方法中将 int 和 double 相乘

Question

In the following program, the user enters a for how many hours they've worked, and b for their hourly rate, then it calculates their pay.

It was working when both a and b were type int , then I realized my teacher asked for b to be a double.

I tried changing everything for b from int to double , but now it is returning an error.

What am I doing wrong?

import java.util.Scanner;

public class Project61 {

  public static void main(String[] args) {
      Scanner in=new Scanner(System.in);
      System.out.println("Enter the amount of hours first and then the hourly rate");
      int a=in.nextInt();
      double b=in.nextDouble();
      double res = mult (a, b);
      System.out.println("Hours : "+ a);
      System.out.println("Rate per hour : "+ "$"+ b);
      System.out.println("Pay : "+ "$" +res);
  }

  public static double mult(int a, double b) {

      if(b ==1){
          return a;
      }
      if (b<1) {
          return -a + mult(a, b+1);
      }
      else{
          return a + mult(a, b-1);
      }
   }


}

Answer 1

The problem is that, if b is not equal to an integer (for instance, if b == 2.5 ), you will never get 1 by repeatedly subtracting 1 from it. So your recursive function will call itself with b == 1.5 , then with b == 0.5 , then again with b == 1.5 , ad infinitum (or at least, ad untilum Javaum runsum outum ofum stackum memoryum). You need to create an exit case that you can guarantee will be triggered eventually.

Answer 2

You have to convert int a to double. You can not multiply double with integer. You could convert int a to double after input or just in

method public static double mult(int a, double b) 
{
  double aa = a.doubleValue();

      if(b ==1)
      {
          return a;
      }
      if (b<1) 
      {
          return -aa + mult(aa, b+1);
      }
      else
      {
          return aa + mult(aa, b-1);
      }
}