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I have been at this for about 5 hours now and I do not know what to do anymore. This homework is due in about 2 hours so I hope someone can help me figure this out. I am not looking for answer. I sincerely want to learn this language but I do need so help. Here is the homework question:
The value ex can be approximated by the sum:
1 + x + x2/2! + x3/3! + ... + xn/n!
Write a program that takes a value x as input and outputs this sum for n taken to be each of the values 1 to 10, 50, and 100. Your program should repeat the calculation for new values of x until the user says she or he is through. The expression n! is called the factorial of n and is defined as
n! = 1 * 2 * 3 * ... * n
Use variables of type double to store the factorials or you are likely to produce integer overflow, that is integers larger than Java allows, (or arrange your calculation to avoid any direct calculation of factorials).
The output is suppose to look something like this:
Enter a value for x (or a blank line to quit):
6
n = 1: e^x = 7
n = 2: e^x = 25
n = 3: e^x = 61
n = 4: e^x = 115
n = 5: e^x = 179.8
n = 6: e^x = 244.6
n = 7: e^x = 300.143
n = 8: e^x = 341.8
n = 9: e^x = 369.571
n = 10: e^x = 386.234
n = 50: e^x = 403.429
n = 100: e^x = 403.429
Enter a value for x (or a blank line to quit):
and this is what I have so far:
import java.util.Scanner;
import java.text.DecimalFormat; // It's okay if you don't use this.
import java.lang.Math;
  Iteratively computes e^x for a given value x, outputing values at iteration
  1 to 10, 50, and 100
public class Ex {
    public static void main(String[] args)  {
        // Make a Scanner to read data from the console
        Scanner console = new Scanner(System.in);
        // Make a NumberFormat object that we'll use when printing values
        // of n in the loop below (use of this format is optional)
        DecimalFormat nFormat = new DecimalFormat("000");
        // Read in a number for x
        System.out.println("Enter a value for x (or a blank line to quit):");
        String xString = console.nextLine();
        while ((xString != null) && (xString.length() > 0)) {
            double x = Double.parseDouble(xString);
            double fact = 1;
          for(int i = 2; i <= x; i++)     // loop
                         fact = fact * i;     // shorthand for: fact = fact * i;
                         System.out.println(fact);
            // Start over again
            System.out.println(
                "Enter a value for x (or a blank line to quit):");
            xString = console.nextLine();
}where do I go from here to sovle this problem?

Answer 1

Have a look at the Math.pow() method. And for what it's worth, many of the most helpful folks around here deliberately overlook threads with subject lines like the one you used. You can get better, faster help by using a descriptive subject line and refraining from slang and abbreviations. Of course, you're free to ignore that advice as well, but it's in your best interest to make your questions interesting to answer and present them in a format that encourages rather than discourages help.
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