foo.c: In function 'main':
foo.c:9:20: warning: implicit declaration of function 'sqrt' [-Wimplicit-function-declaration]
    9 |         for(i=1;i<=sqrt(a);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:9:20: warning: incompatible implicit declaration of built-in function 'sqrt' [-Wbuiltin-declaration-mismatch]
    9 |         for(i=1;i<=sqrt(a);i++)
      |                    ^~~~
foo.c:9:20: note: include '<math.h>' or provide a declaration of 'sqrt'

[Hydro](https://hydro.ac)提供评测服务