1 #include <stdio.h>
 2 #include<math.h> 
 3 int main()
 4 {    
 5     int n,p,q;
 6     scanf("%d",&n);
 7     q=sqrt(n);
 8     int isPrimer = 1;
 9     for(p=2;p<=q;p++)
10         if(n%p==0) 
11             isPrimer = 0;
12     if(isPrimer==1)
13         printf("%d is a prime!\n",n);    
14     else
15         printf("%d is not a prime!\n",n);
16     
17     return 0;
18 }

 1 #include <stdio.h>
 2 #include<math.h> 
 3 int main()
 4 {    
 5     int n,p,q;
 6     scanf("%d",&n);
 7     q=sqrt(n);
 8     for(p=2;p<=q;p++)
 9         if(n%p==0) break;
10     if(p>q)
11         printf("%d is a prime!\n",n);    
12     else
13         printf("%d is not a prime!\n",n);
14     return 0;
15 }