foo.c: In function 'max':
foo.c:14:1: warning: control reaches end of non-void function [-Wreturn-type]
   14 | }
      | ^
foo.c: In function 'main':
foo.c:18:2: warning: ignoring return value of 'scanf', declared with attribute warn_unused_result [-Wunused-result]
   18 |  scanf("%d %d",&a1,&b1) ;
      |  ^~~~~~~~~~~~~~~~~~~~~~
foo.c:19:2: warning: ignoring return value of 'scanf', declared with attribute warn_unused_result [-Wunused-result]
   19 |  scanf("%d %d",&a2,&b2) ;
      |  ^~~~~~~~~~~~~~~~~~~~~~

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