# Separating Composite and Prime Numbers in Java

Write a program to input any n numbers in a single dimensional array arr[], now store all the prime numbers in the array prim[] and all the composite numbers in the array com[]. Display the contents of both the arrays prim[] and com[].

Program:

``````import java.io.*;
class Arrange{
public static void main(String args[])
throws IOException{
System.out.print("Number of elements: ");
int arr[] = new int[n];
int i = 0;
int j = 0;
int k = 0;
int countc = 0;
int countp = 0;
for(i = 0; i < arr.length; i++){
System.out.print("Enter element: ");
if(isPrime(arr[i]))
countp++;
else
countc++;
}
int prim[] = new int[countp];
int com[] = new int[countc];
for(i = 0; i < arr.length; i++){
if(isPrime(arr[i]))
prim[j++] = arr[i];
else
com[k++] = arr[i];
}
System.out.println("Prime Numbers:");
for(i = 0; i < prim.length; i++)
System.out.print(prim[i] + "\t");
System.out.println("\nComposite Numbers:");
for(i = 0; i < com.length; i++)
System.out.print(com[i] + "\t");
}
public static boolean isPrime(int n){
int f = 0;
for(int i = 1; i <= n; i++)
if(n % i == 0)
f++;
if(f == 2)
return true;
return false;
}
}``````

## 4 thoughts on “Separating Composite and Prime Numbers in Java”

1. sayan rana on said:

Sir,in the above program,the output is showing like this:
Number of elements: 10
Enter element: 1
Enter element: 2
Enter element: 3
Enter element: 4
Enter element: 5
Enter element: 6
Enter element: 7
Enter element: 8
Enter element: 9
Enter element: 10
Prime Numbers:
2 3 5 7
Composite Numbers:
1 4 6 8 9 10
As you have told 1 is neither prime nor composite but 1 is being displayed in the composite array.Sir,can you please explain why is it so?

• admin on said:

In that case, write a separate if statement for 1 to avoid putting it in the array.

2. sayan rana on said:

Sir,In the above program if we accept 1 as element of the array,in which array will it display prime or composite?

• admin on said:

1 is unique. It is neither prime nor composite.

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