Question

how to write a c++ program to check whether a given number is prime or not?

Answer 1

Here is the algorithm http://en.wikipedia.org/wiki/Miller%E2%80%93Rabin_primality_test
Try to understand the logic, start writing the program, and i am sure people will help you here if you get stuck -_-

Answer 2

At what point are you having difficulties, with the language, the algorithm, or compliation?

Answer 3

int num,i,flag=1;
cin>>num;

for(i=num;i>0;i--)
{
if(i%num ==0)
{flag=0;}
}

if(flag == 0)
{cout<<"composite";}
if(flag == 1)
{cout<<"prime";}