a bit confuse about this java code

Question

import java.util.Scanner;
class PrimeCheck
{
public static void main(String args[])
{
int temp;
boolean isPrime=true;
Scanner scan= new Scanner(System.in);
System.out.println("Enter any number:");
//capture the input in an integer
int num=scan.nextInt();
scan.close();
for(int i=2;i<=num/2;i++)
{
temp=num%i;
if(temp==0)
{
isPrime=false;
break;
}
}
//If isPrime is true then the number is prime else not
if(isPrime)
System.out.println(num + " is a Prime Number");
else
System.out.println(num + " is not a Prime Number");
}
}

ques : I am a bit confuse about the (for loop) why there is a i<=num/2 .. why num is divided by 2 .. like if my num is 10 diving it would be 5 which is a primal number right? while 10 is not.n on the next line num variable shouldn't be effected. but sill why divide by2

Answer 1

Every divisor greater than 1/2 of a number obviously cannot be a factor of it*. So for the 10, 10/2 = 5 will also be evaluated, but not the 6.

edit: * except itself, which is excluded for prime numbers

Answer 2

because after num/2 result of num%i will not be 0

13 = 2x6 +1
13 = 1x7 +6
13 = 1x8 +5
13 = 1x9 +4
13 = 1x10+3

Answer 3

so can i use i<= num /i instead of 2..since the value is same?

Answer 4

No, because it will not keep the value 2, it is increased each iteration.

Answer 5

ohh.. gottcha