prime no. function problem

Question

int isPrime(int num)
{
int i;

for(i=2; i<=num/2; i++)
{

if(num % i == 0)
{
return 0;
}
}

return 1;
}

why i<=num/2 ?
also some uses i=sqrt(num) ? as end condition

Answer 1

Thank you for answering