import java.io.*;
public class Prime{
    public static void main(String[] args) throws IOException {
    	BufferedReader jill = new BufferedReader (new InputStreamReader (System.in));
        boolean isPrime = true;
        	System.out.print("Enter number: ");
        	int input = Integer.parseInt(jill.readLine());
	        if(input < 2){
	        	isPrime = false;
	        }
        	if (input == 2) {
	            isPrime = true;
	        }
	        if (isPrime)
	            for (int y=3; y<=(input/2); y+=2)
	                if(input == 3){
	                	isPrime = true;
	                	break;
	                }
	                else if (input % y == 0)
	                {
	                    isPrime = false;
	                    break;
	                }
	        if (isPrime) 
	        	System.out.println("That is a prime number.");
	        else{
	        	System.out.println("That is not a prime number.");
	        }
	     
	    
       }
        	 
}

// i was able to determine whether it is a prime number or not. but my problem is i want to count how many prime number in a given range..
//exampe: the user gave range 10. there are 4 prime numbers: 2, 3, 5, and 7..
..//help me!

// i was able to determine whether it is a prime number or not.

Your program to find a prime number is incorrect.

Firstly the program written is not able to handle any prime number entered, you should correct that ex: Try entering 5 .....

Also follow good coding standatrds where necessary - Like including braces

And finding the numbers for a range would be easy using the logic.....

try this code. its result is correct for 10 i dont know for other nos..

public class Prime {
	public static void primeNo(int x){
		for (int i = 1; i <= x; i++){
			int ctr = 0;
			for(int y = 1; y<=i; y++){
				if(i%y == 0){
					ctr++;
				}
			}
			if (ctr == 2){
				System.out.println(i);
			}
		}
	}
	
	public static void main(String[] args) {
		primeNo(10);
	}
}
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