Hello Everybody,

I am suppose to "write a Java program that reads a positive integer n from standard input, then prints out the first n prime number." It's divided into 3 parts.

1st: This function will return true or false according to whether m is prime or composite. The array argument P will contain a sufficient number of primes to do the testing. Specifically, at the time isPrime() is called, array P must contain (at least) all primes p in the range 2 p m . For instance, to test m = 53 for primality, one must do successive trial divisions by 2, 3, 5, and 7. We go no further since 11 > 53 . Thus a precondition for the function call isPrime(53, P) is that P[0] = 2 , P[1] = 3 , P[2] = 5, and P[3] = 7 . The return value in this case would be true since all these divisions fail. Similarly to test m =143 , one must do trial divisions by 2, 3, 5, 7, and 11 (since 13 > 143 ). The precondition for the function call isPrime(143, P) is therefore P[0] = 2 , P[1] = 3 , P[2] = 5, P[3] = 7 , and P[4] =11. The return value in this case would be false since 11 divides 143. Function isPrime() should contain a loop that steps through array P, doing trial divisions. This loop should terminate when 2 either a trial division succeeds, in which case false is returned, or until the next prime in P is greater than m , in which case true is returned.

Then there is the "main function" • Check that the user supplied exactly one command line argument which can be interpreted as a positive integer n. If the command line argument is not a single positive integer, your program will print a usage message as specified in the examples below, then exit. • Allocate array Primes[] of length n and initialize Primes[0] = 2 . • Enter a loop which will discover subsequent primes and store them as Primes[1] , Primes[2], Primes[3] , ……, Primes[n -1] . This loop should contain an inner loop which walks through successive integers and tests them for primality by calling function isPrime() with appropriate arguments. • Print the contents of array Primes[] to stdout, 10 to a line separated by single spaces. In other words Primes[0] through Primes[9] will go on line 1, Primes[10] though Primes[19] will go on line 2, and so on. Note that if n is not a multiple of 10, then the last line of output will contain fewer than 10 primes.

The last function is called "usage" which I am not sure how to execute this! Your program will include a function called Usage() having signature static void Usage() that prints this message to stderr, then exits. Thus your program will contain three functions in all: main(), isPrime(), and Usage(). Each should be preceded by a comment block giving it’s name, a short description of it’s operation, and any necessary preconditions (such as those for isPrime().)

And hear is my code, but I am having a bit of a problem and could you guys help me fix it? If I enter the number "5" it gives me the prime numbers which are "6,7,8,9" which doesn't make much sense.

import java.util.; import java.io.; import java.lang.*;

public class PrimeNumber { static boolean isPrime(int m, int[] P){ int squarert = Math.round( (float)Math.sqrt(m) ); int i = 2; boolean ans=false; while ((i<=squarert) & (ans==false)) { int c= P[i]; if (m%c==0) ans= true; else ans= false; i++; } /* if(ans ==true) ans=false; else ans=true; return ans; }
///****main

public static void main(String[] args ) { Scanner in= new Scanner(System.in); int input= in.nextInt(); int i, j; int squarert; boolean ans = false; int userNum; int remander = 0; System.out.println("input: " + input); int[] prime = new int[input]; prime[0]= 2; for(i=1; i

  ans = isPrime(j,prime);
j++;}
prime[i] = j;

} //prnt prime System.out.println("The first " + input + " prime number(s) are: "); for(int r=0; r

}//end of main }

Thanks for the help