foo.c: In function 'main':
foo.c:10:34: warning: implicit declaration of function 'sqrt' [-Wimplicit-function-declaration]
   10 |                 for (i = 2; i <= sqrt(n); i++)
      |                                  ^~~~
foo.c:2:1: note: include '<math.h>' or provide a declaration of 'sqrt'
    1 | #include <stdio.h>
  +++ |+#include <math.h>
    2 | 
foo.c:10:34: warning: incompatible implicit declaration of built-in function 'sqrt' [-Wbuiltin-declaration-mismatch]
   10 |                 for (i = 2; i <= sqrt(n); i++)
      |                                  ^~~~
foo.c:10:34: note: include '<math.h>' or provide a declaration of 'sqrt'

[Hydro](https://hydro.ac)提供评测服务