can anyone please make me understand the "for" part of this code...(why we hav taken "j<=i/2" and why we hav used two loops?

Question

// code for printing a range of primary numbers
#include <iostream>
using namespace std;

int main()
{
int n,cnt=1,i=3,flag;
cout<<"How many numbers? ";
cin>>n;
cout<<"\nFirst "<<n<<" Prime numbers:"<<endl;
cout<<"2";
while(cnt<n)
{
flag=0;
for(int j=2;j<=i/2;j++)
if(i%j==0)
{
flag=1;
break;
}
if(flag==0)
{
cout<<", "<<