foo.c:3:1: warning: return type defaults to 'int' [-Wimplicit-int]
    3 | main()
      | ^~~~
foo.c: In function 'main':
foo.c:6:5: warning: ignoring return value of 'scanf', declared with attribute warn_unused_result [-Wunused-result]
    6 |     scanf("%d",&n);
      |     ^~~~~~~~~~~~~~
foo.c:11:13: warning: ignoring return value of 'scanf', declared with attribute warn_unused_result [-Wunused-result]
   11 |             scanf("%d",&a[i][j]);
      |             ^~~~~~~~~~~~~~~~~~~~
foo.c:14:5: warning: 'res' may be used uninitialized in this function [-Wmaybe-uninitialized]
   14 |     printf("%.3f",res);
      |     ^~~~~~~~~~~~~~~~~~

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