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Thread: Need help people please help!!

  1. #1
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    Default Need help people please help!!

    Hello everyone i need help with a prime number program i'm getting a small error and don't know how to solve it
    // File: Prime.java                                                        |
    // ------------------------------------------------------------------------+
    // Author:  Shane Lowry                           Group: Group 1           |
    // Student# B00059978                              Date: 13/11/2012        |
    // ------------------------------------------------------------------------+
    // Problem Set 2:  Problem 9                                               |
    //                                                                         |
    // DESCRIPTION:                                                            |
    // Input a number and output if is a prime number is equal to 1.           |
    //                                                                         |
    //                                                                         |
    // ------------------------------------------------------------------------+
    import java.io.*;
    import java.util.*;
     
    public class Prime
    {
       public static void main(String[] args)throws IOException
       {
           // Set up an input buffer for reading input values
           BufferedReader input = new BufferedReader(new InputStreamReader(System.in));
           int i;
     
           // Set up an output buffer for writing results to
           PrintWriter output = new PrintWriter(System.out);
     
           // Read in input values
           String line1 = input.readLine();
     
     
           // Convert string into binary
           int x = Integer.parseInt(line1);
     
           // Output input values
           output.println("Prime Number: ");
           for(i=1; i<x; i++){
              int j;
              for(j=2;j<i; j++){
               int n = i%j;
    	         if(n==0)
    	           break;
               }
            }
            if(i == j){
            output.println(" "+i);}
     
    			 // clean up output buffer
           output.flush();
      }
    }
    Here's the error i keep getting
    C:\Users\shane\Documents\Algorithem\Week 2 Problems\Prime.java:44: error: cannot find symbol
    if(i == j){
    ^
    symbol: variable j
    location: class Prime
    1 error


  2. #2
    Super Moderator curmudgeon's Avatar
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    Default Re: Need help people please help!!

    This is a scoping problem. The variable j is only visible within the scope of where it was declared. Thus it is only visible within the for loop as it was declared in there, and doesn't exist after the for loop ends (after the closing brace of the for loop).

  3. #3
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    Default Re: Need help people please help!!

    can someone help me i'm trying to print out prime numbers starting with 1 but it doesn't print out 1 i know it maybe a stupid question but i can't seem to find out how to

  4. #4
    Super Moderator pbrockway2's Avatar
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    Default Re: Need help people please help!!

    If you want someone to suggest why the code you're using doesn't output 1, then you'll have to post the code you're using...

    Also note that 1 isn't a prime number.

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    Default Re: Need help people please help!!

    ok sorry here's the code and are sure about 1 not being a prime number
    // File: Prime.java                                                        |
    // ------------------------------------------------------------------------+
    // Author:  Shane Lowry                           Group: Group 1           |
    // Student# B00059978                              Date: 13/11/2012        |
    // ------------------------------------------------------------------------+
    // Problem Set 2:  Problem 9                                               |
    //                                                                         |
    // DESCRIPTION:                                                            |
    // Input a number and output if is a prime number is equal to 1.           |
    //                                                                         |
    //                                                                         |
    // ------------------------------------------------------------------------+
    import java.io.*;
    import java.util.*;
     
    public class Prime
    {
       public static void main(String[] args)throws IOException
       {
           // Set up an input buffer for reading input values
           BufferedReader input = new BufferedReader(new InputStreamReader(System.in));
     
           // Set up an output buffer for writing results to
           PrintWriter output = new PrintWriter(System.out);
     
           // Read in input values
           String line1 = input.readLine();
     
     
           // Convert string into binary
           int X = Integer.parseInt(line1);
           int i;
     
     
           // Output input values
           for(i=0;i<=X; i++){
              int j;
              for(j=2;j<i; j++){
    					 int n = i%j;
    	         if(n==0){
    	           break;
    	        }
    	      }
            if(i == j){
            output.println(" "+i);}
           }
     
           // clean up output buffer
           output.flush();
      }
    }

  6. #6
    Super Moderator pbrockway2's Avatar
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    Default Re: Need help people please help!!

    if(i == j){
        output.println(" "+i);}
    }

    We can be quite sure that won't print a "1" because j has just gone through a for loop where it was set to 2 and made to increment.

    Prime number - Wikipedia, the free encyclopedia The first sentence should be enough. But there's a section on whether one is considered a prime.

  7. #7
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    Default Re: Need help people please help!!

    so my code is right but do i have to set j = 1 ? please help im very confused

  8. #8
    Super Moderator pbrockway2's Avatar
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    Default Re: Need help people please help!!

    Try it and see. Better yet guess first: what do you think i%j will yield if j is 1? And how will that affect the numbers you report as prime.

    Personally I don't regard 1 as prime, but if you must, just print it before you start all the looping business.

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