foo.cc: In function 'int main()':
foo.cc:36:9: warning: unused variable 'k' [-Wunused-variable]
 int i,j,k;
         ^
foo.cc:41:6: warning: ignoring return value of 'int scanf(const char*, ...)', declared with attribute warn_unused_result [-Wunused-result]
 scanf("%lf%lf",&a[i].x,&a[i].y);
 ~~~~~^~~~~~~~~~~~~~~~~~~~~~~~~~

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