daydream

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.

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RelaX

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?

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hrdwareguy

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.

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Cuball

hmm common, that's easy

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

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daydream

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

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"Can't help it if I space in a daze, my eyes tune out the other way... I may switch off and go in a daydream... in this head my thoughts are deep, Sometimes I can't even speak, would someone be and not pretend, I'm off again in my world"

daydream

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?

__________________
"Can't help it if I space in a daze, my eyes tune out the other way... I may switch off and go in a daydream... in this head my thoughts are deep, Sometimes I can't even speak, would someone be and not pretend, I'm off again in my world"

firebirdta

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.

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feelgood

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.

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dnd

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.

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dnd

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

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daydream

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

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
}
}

__________________
"Can't help it if I space in a daze, my eyes tune out the other way... I may switch off and go in a daydream... in this head my thoughts are deep, Sometimes I can't even speak, would someone be and not pretend, I'm off again in my world"