foo.c: In function 'Insert_key':
foo.c:19:1: warning: control reaches end of non-void function [-Wreturn-type]
   19 | }
      | ^
foo.c: In function 'main':
foo.c:23:5: warning: ignoring return value of 'scanf', declared with attribute warn_unused_result [-Wunused-result]
   23 |     scanf("%d\n",&n);
      |     ^~~~~~~~~~~~~~~~
foo.c:27:9: warning: ignoring return value of 'scanf', declared with attribute warn_unused_result [-Wunused-result]
   27 |         scanf("%d",&array[i]);
      |         ^~~~~~~~~~~~~~~~~~~~~
foo.c:29:5: warning: ignoring return value of 'scanf', declared with attribute warn_unused_result [-Wunused-result]
   29 |     scanf("%d",&key);
      |     ^~~~~~~~~~~~~~~~

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