foo.c: In function 'aaa':
foo.c:9:12: error: 'x' undeclared (first use in this function)
    9 |     return x;
      |            ^
foo.c:9:12: note: each undeclared identifier is reported only once for each function it appears in
foo.c:10:1: warning: control reaches end of non-void function [-Wreturn-type]
   10 | }
      | ^
foo.c: In function 'main':
foo.c:16:2: warning: ignoring return value of 'scanf', declared with attribute warn_unused_result [-Wunused-result]
   16 |  scanf("%d %d",&b1,&a1);
      |  ^~~~~~~~~~~~~~~~~~~~~~
foo.c:17:2: warning: ignoring return value of 'scanf', declared with attribute warn_unused_result [-Wunused-result]
   17 |  scanf("%d %d",&b2,&a2);
      |  ^~~~~~~~~~~~~~~~~~~~~~

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