foo.c: In function 'main':
foo.c:15:19: error: 'a' undeclared (first use in this function)
   15 |         for(int i=a;i<=b;i++)
      |                   ^
foo.c:15:19: note: each undeclared identifier is reported only once for each function it appears in
foo.c:15:24: error: 'b' undeclared (first use in this function)
   15 |         for(int i=a;i<=b;i++)
      |                        ^
foo.c:20:20: error: 'j' undeclared (first use in this function)
   20 |                 if(j<=sqrt(i))
      |                    ^

[Hydro](https://hydro.ac)提供评测服务