Program to check whether a number is Prime Or Not

#include"stdio."
int main()
{
int n,flag=0,i;

printf("Enter a number:");
scanf("%d",&n);

if(n<=1)
printf("Not prime nor composite");
else
{
for(i=2;i<=n/2;i++)
{
if((n%i)==0)
{
flag=1;
break;
}
}
if (flag==0)
printf("Prime");
else
printf("Not Prime");
}