foo.cc: In function 'double getd(int, int)':
foo.cc:24:14: error: 'fabs' was not declared in this scope
     double x=fabs(a[i].x-a[j].x);
              ^~~~
foo.cc:24:14: note: suggested alternative: 'labs'
     double x=fabs(a[i].x-a[j].x);
              ^~~~
              labs
foo.cc:26:12: error: 'sqrt' was not declared in this scope
     return sqrt(x*x+y*y);
            ^~~~
foo.cc:26:12: note: suggested alternative: 'qsort'
     return sqrt(x*x+y*y);
            ^~~~
            qsort

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