foo.c: In function 'main':
foo.c:10:25: warning: implicit declaration of function 'sqrt' [-Wimplicit-function-declaration]
   10 |                 int n = sqrt(x);
      |                         ^~~~
foo.c:2:1: note: include '<math.h>' or provide a declaration of 'sqrt'
    1 | #include<stdio.h>
  +++ |+#include <math.h>
    2 | int main()
foo.c:10:25: warning: incompatible implicit declaration of built-in function 'sqrt' [-Wbuiltin-declaration-mismatch]
   10 |                 int n = sqrt(x);
      |                         ^~~~
foo.c:10:25: note: include '<math.h>' or provide a declaration of 'sqrt'

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