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[klagartin]

Okay, So I was assigned a project for school.
It is to prompt the user to enter a fixed number of points, declare the max and min X values, then plug x into an equation for y and print it. I've been able to successfully do that.

Here my problem: I get this exact error

Exception in thread "main" java.lang.ArrayIndexOutOfBoundsException: 5
at locZero.main(locZero.java:41)

This comes into play at line 41 when im trying to use if statements and another array to record where the y values change signs from pos to neg/vise versa.

Here is the code

import java.util.Scanner;

public class locZero{
	public static void main(String[]args){
		
		Scanner input= new Scanner(System.in);
		
		double minX, maxX;
		int numPoints;
		int numChange=0;
		
		System.out.print("Enter number of points: ");
		numPoints=input.nextInt();
		System.out.print("Enter min x: ");
		minX=input.nextDouble();
		System.out.print("Enter max x: ");
		maxX=input.nextDouble();
		
		
		double [] x= new double[numPoints];
		double [] y= new double[numPoints];
		double [] change= new double[numPoints];
		
		System.out.println("i"+"\t"+"x[i]"+"\t"+"y[i]");
		
		for(int i=0;i<numPoints;i++){
			System.out.print(i+"\t");
			
			x[0]=minX;
			x[numPoints-1]= maxX;
			x[i]=x[0]+i*((maxX-minX)/(numPoints-1));			
			y[i]=(((x[i])*(x[i])*(x[i]))-(2*((x[i])*(x[i])))-(5*x[i])+4);
			
		
			System.out.print(x[i]);
			System.out.print("\t");
			System.out.print(y[i]);
			System.out.println();
			
			for(i=0;i<=numPoints;i++){
				if(y[i]>=0 && y[i+1]<0){
					change[numChange]=i;
					numChange++;
				}
				else if(y[i]>0 && y[i+1]<=0){
					change[numChange]=i;
					numChange++;
				}
		
			}
		}
	
		
	}
		
}

please try to help me. I know the error means im using an array that does exist, but i dunno how i am.

[Old Pedant]

			for(i=0;i<=numPoints;i++){
				if(y[i]>=0 && y[i+1]<0){
					change[numChange]=i;
					numChange++;
				}
				else if(y[i]>0 && y[i+1]<=0){

Your other loops only went to i < numPoints. With this loop, you are guaranteed to be 1 past the end of the array.

But then you make it worse:
How can you use i+1 if i is already at or past the maximum value for the array subscript??