Possible loss of precision error with an array in a loop

Question

So I keep getting errors similar to this in a few programs and I can't quite figure it out. The array and all variables in the loop are double, so I don't get why it expects an int value. Anyway here it is, all the errors refer to the for statement in the last block:

 import java.util.Scanner;

    public class Exercise610
    { public static void main (String[] args)
        {
        int smallest;
        Scanner stdIn = new Scanner (System.in);
        double array1 [] = new double [100]; 
        for (int i=0; array1[i] != -7; i++)
        {
            System.out.println("Input a value in yer string, or -7 to end");
            array1[i] = stdIn.nextDouble();
        }

        smallest = indexOfSmallestElement(array1);
        System.out.println("The smallest value in the array is " + smallest);
    }


    public static int indexOfSmallestElement (double[] array)
    {
        int smallestInt;
        double smallest = array[0];
        for (double u: array)
        {
            if (array[u+1] < array[u])
            {
                smallest = array[u+1];
            }
        }
        smallestInt = (int) smallest;
        return smallestInt;
    }
}

File: /Users/Crbn/introcs/Exercise610.java [line: 33]
Error: /Users/Crbn/introcs/Exercise610.java:33: possible loss of precision
found : double
required: int
File: /Users/Crbn/introcs/Exercise610.java [line: 33]
Error: /Users/Crbn/introcs/Exercise610.java:33: possible loss of precision
found : double
required: int
File: /Users/Crbn/introcs/Exercise610.java [line: 35]
Error: /Users/Crbn/introcs/Exercise610.java:35: possible loss of precision
found : double
required: int

Answer 1

You cannot say array[u+1] as this refers to the index of an array. The errors are because u is a double and the indices in any array are numbers in integers from 0, 1, 2 etc...

You should loop through an array using integers like:

for (int i = 0; i < something; i++){
    // do something here
}

You can cast u to an int if you want (see below code) but better to declare it int to begin with.

 for (double u : array) {
            if (array[(int) (u + 1)] < array[(int) u]) {
                smallest = array[(int) (u + 1)];
            }
        }

The reason for the loss of precision error is because an int occupies 32 bits of memory, a double occupies 64 bits, so if you try and squeeze a double into an int you may lose some data.

Answer 2

I'm not familiar with Java, but I think it could be something to do with this line smallestInt = (int) smallest; - basically it is letting you know that casting a double to an int will result in the loss of data.

I suspect your method is either named wrong or coded wrong, the method name suggests that you should be returning the index, not the value.

smallest = array[u+1]; is assigning the array value, not the array index - this might actually be your problem, you possibly want smallest = u + 1; given the method name.