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Thread: Help! Factoring application
 11012009, 08:03 PM #1Member
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Help! Factoring application
Hi everyone, I enrolled in APCS this year and am new to java. So far I have been able to do all my projects with ease however this one seems difficult. Here is what my teacher wants the code to look like:

Sample Output:
Please enter an integer: 150
Factored:
150 = 2 x 3 x 5 x 5

Could someone please help me? Here are some rules: we have not learned/not supposed to use arrays (idk if that helps), we know switch statements, for/do/while loops, ifstatements, scanner class, math class, and some other stuff. Oh and this has to be done in java. Please respond as soon as possible. Thanks!
 11012009, 08:06 PM #2Member
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also it has to work for all numbers not just 150
 11012009, 08:09 PM #3
 11012009, 08:13 PM #4Member
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Something like this?
Java Code:int number = 150; int factor = 0; for(int i = 2; i <= number; i++) { if((number % i) == 0) { factor = i; break; } } if(factor != 0) { System.out.println("Factored: "+number+" = "+factor+" x "+number/factor); } else { System.out.println("Not possible."); }
 11012009, 08:16 PM #5Member
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i tried doing an extensive number of if statements but that hasn't worked because there are an infinite number of prime numbers, so I deleted the code
 11012009, 08:18 PM #6Member
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yeah i think that might work
thanks!
 11012009, 08:31 PM #7Member
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hmm i need to find a way to eliminate all none prime numbers
my code looks like:
import java.util.Scanner;
import java.text.DecimalFormat;
public class factor{
public static void main (String[] args) {
//This is my declaration section
int user_input, factor;
Scanner scan = new Scanner(System.in);
//This section receives the users input
System.out.print ("Please enter an integer to be factored:");
user_input = scan.nextInt();
System.out.println ("Factored:");
System.out.print (user_input + " = ");
for (int i = 2; i < user_input; i++) {
if ((user_input % i) == 0) {
factor = i;
System.out.print (factor + " x ");
}
}
}
}
The output for 24 with this code is:
Please enter an integer to be factored: [24]
Factored:
24 = 2 x 3 x 4 x 6 x 8 x 12 x
Also how do i get rid of that extra multiplication sign
 11012009, 08:35 PM #8Member
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Also 25 returns as 5 x
how do i have it return as 5 x 5
 11012009, 08:35 PM #9Member
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Code tags please.
 11012009, 08:41 PM #10Member
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what are code tags?
sorry
 11012009, 08:44 PM #11Member
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Put [ CODE ] and [ /CODE ] around your code. (without the spaces)
 11012009, 08:50 PM #12Member
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code looks like this so far:
Java Code:import java.util.Scanner; import java.text.DecimalFormat; public class factor{ public static void main (String[] args) { //This is my declaration section int user_input, factor; Scanner scan = new Scanner(System.in); //This section receives the users input System.out.print ("Please enter an integer to be factored:"); user_input = scan.nextInt(); System.out.println ("Factored:"); System.out.print (user_input + " = "); for (int i = 2; i < user_input; i++) { if ((user_input % i) == 0) { factor = i; System.out.print (factor + " x "); } } } }
 11012009, 08:55 PM #13Member
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Try this as a method.
Java Code:public method getNextFactor(int number) { int factor = 0; for (int i = 2; i < number; i++) { if ((number % i) == 0) { factor = i; break; } } return factor; }
 11012009, 09:58 PM #14Member
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OP seems to have the right idea on displaying his ouput. Will leave it to him to figure that out.
What I have noticed is that he is incrementing his factor after he verifies that it is a factor. This will not be correct.
Consider a number like 40 (2 x 2 x 2 x5);
You will find 2, increment to 3 (not a factor), then increment to 4 which is a factor. But 4 is 2 x 2. You need to loop with the value 2 until you find that it is no longer a factor. Don't worry about the number being prime. You will find them as you progress in the algorithm.
http://en.wikipedia.org/wiki/Sieve_of_Eratosthenes
The sieve of eratosthenes merely finds the primes, but the reference will help you understand what you are doing.
Java Code:Factor(X) n=2 while (not end condition) if (n is a factor of X) { add n to factor list X = X / n } // if while(n is a factor of X { add n to factor list X = X / n } //while if(( X equals 1) ){ end condition = true } //if increment n } //while end Factor
"X" MUST be 1 on the last iteration, or there is another prime factor
edit:Last edited by rdtindsm; 11022009 at 05:15 AM. Reason: logic error
 11022009, 03:07 AM #15Member
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thanks for all the hel
 11022009, 03:09 AM #16Member
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sorry i meant "help" not "hel"
 11022009, 03:15 AM #17
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Hi blueduiker, if you have free time please read our FAQ page. You can find lots of useful things from there.
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