foo.c: In function 'main':
foo.c:6:6: warning: unused variable 'i' [-Wunused-variable]
  int i;
      ^
foo.c:9:2: warning: ignoring return value of 'scanf', declared with attribute warn_unused_result [-Wunused-result]
  scanf("%d %d", &x1, &x2);
  ^~~~~~~~~~~~~~~~~~~~~~~~
foo.c:10:2: warning: ignoring return value of 'scanf', declared with attribute warn_unused_result [-Wunused-result]
  scanf("%d %d", &y1, &y2);
  ^~~~~~~~~~~~~~~~~~~~~~~~

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