foo.c: In function 'main':
foo.c:8:2: error: 'sum' undeclared (first use in this function)
  sum=xmax+xmin;
  ^~~
foo.c:8:2: note: each undeclared identifier is reported only once for each function it appears in
foo.c:7:2: warning: ignoring return value of 'scanf', declared with attribute warn_unused_result [-Wunused-result]
  scanf("%d%d",&xmin,&xmax);
  ^~~~~~~~~~~~~~~~~~~~~~~~~

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