[java] need help w/small program
 

I need to write a program that allows a user to input a number and then output the factorial. (eg. user inputs 5 and program outputs 5!=5*4*3*2*1=120) then the program has to repeat so the user can continue to enter numbers until the user enters -999. This will stop the program.

Any help would be appreciated... I'm really stuck on this one. I don't really have any experience with java. :confused:

This sounds like a "do my homework for me please" post...
It isn't very difficult if you imlement the factorial computational recursively, but why would any sane man/woman need a factorial calculator in Java?

EDIT: actually... thinking about it... I was given an assignment exactly like this in my first year... or was it second?

How about you post some of your code and tell us where you are stuck at so we can point you in the right direction.

hmm common, that's easy

int result = 1;
for (int i=n; i>n; i--)
result *=i;

Ok so here is what I have so far... It's not giving me the correct answer and I can't get it to loop... I also have to try to make it so when a user inputs -999 the program will stop...

package proj3laa;
import javax.swing.*;
import java.text.*;
public class Factorial
{
public static void main(String[] args)
{
int num;
int factorial;
factorial=1;
num=1;
String s1;
s1=JOptionPane.showInputDialog("Input a number");
num=Integer.parseInt(s1);

while (num>=0 && num!=-999)
{//start while
factorial= num*(num-1);
System.out.print(factorial);
num--;
}//end while
}
}

*edit- well I figured out how to allow a user to input a number and then the prog outputs all of the numbers below it. (ex user inputs 5 prog outputs: 543231) But i dont know how to get it to multiply those numbers. or anywhere close to what I need it to do besides that....

int factorial;
String s1;
factorial=1;
s1=JOptionPane.showInputDialog("Input a number");
factorial=Integer.parseInt(s1);

while (factorial >0)
{//start while
System.out.print (factorial);
factorial--;
}//end while
:crazy:

oh wait... ok so I think that I need to use a for loop for this instead... I tried something like what cubal said...

int n;
i=n;
int total = 1;

for (i>n;i>0;i--)
total = total*i;

but just writing that isn't working... I'm getting a red line for an error under the n in the for loop. is this right? am i missing something?

Are you writing this program for a class? If so, you should speak to whoever is teaching it because you are making basic syntax mistakes.

http://www.eimc.brad.ac.uk/java/tuto...ect/2/loop.htm

Go to that link and read about looping. Go from there.

Here's your anwer:
int i;
for(i = n; i > n; i--)
i*=i;

System.out.println("Factorial Result: " + i);

Here's the problem with your program:
You need to assign the i value. When creating the for loop statement, it works as this way
For(set variables; set limits of the variable; iteration)

for example

for(int i = 0; i < 20; i++)
{
System.out.println(i);
}

I don't understand why you need to assign i = n, nor do I see any need to have total = 1. You can still use i to get the result.

now i'm sure swing was never a first/second term module. i'm pretty sure this is just a command line program that u want, and in that case get rid of your JOptionPane etc.

i think it was something like this, any mistakes sorry, i just tried to knock it up quick for u:

if (n <0) {
System.out.println("Error, negative number !");
System.exit(-1);
}
//check exit condition
if (n == 999) {
System.out.println("Exiting");
System.exit(1);
}
// Check for zero
if (n == 0) {
System.out.println("The factorial of zero is one.");
System.exit(-2);
}
// Compute
for ( count = 1; count <= n; count++) {
fact*= count;
}

// print result
System.out.println("The factorial of " + n + " is : " + fact + ".");


all u need to do is take in the user input from the command line with args[0] and check what the number is

thanks a lot for your help everyone! I finally figured out my program! :D

package proj3;
import javax.swing.*;
import java.text.*;
public class factorial {
public static void main(String[] args) {
String s1;
int num1,total;
num1=0;
total=1;
s1=JOptionPane.showInputDialog("Enter a number to calculate its factorial.\nEnter -999 to exit the program");
num1=Integer.parseInt(s1);
while(num1!=-999)
{//start while loop 1
System.out.print(num1 + "!=");
while ((num1 > 1) && (num1 != -999))
{ //start of while statement 2
System.out.print(num1 + "*");
total = (total * num1);
num1--;
} //end of while statement 2
System.out.print("1=");
System.out.println(total);
System.exit(0);
}//end while loop 1
}
}