foo.c: In function 'Add':
foo.c:70:7: error: 'i' undeclared (first use in this function)
   for(i;i<n;i++)
       ^
foo.c:70:7: note: each undeclared identifier is reported only once for each function it appears in
foo.c: In function 'main':
foo.c:11:2: warning: ignoring return value of 'scanf', declared with attribute warn_unused_result [-Wunused-result]
  scanf("%d%d%d%d",&x1,&n1,&x2,&n2);
  ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

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