foo.c: In function 'main':
foo.c:13:11: warning: format '%d' expects argument of type 'int *', but argument 2 has type 'long long int *' [-Wformat=]
   scanf("%d",&a[i]);
          ~^  ~~~~~
          %lld
foo.c:17:11: warning: format '%d' expects argument of type 'int', but argument 2 has type 'long long int' [-Wformat=]
  printf("%d\n",(a[0]*a[3]+a[1]*a[2])%(int)(1e9+7));
          ~^    ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
          %lld
foo.c:13:3: warning: ignoring return value of 'scanf', declared with attribute warn_unused_result [-Wunused-result]
   scanf("%d",&a[i]);
   ^~~~~~~~~~~~~~~~~

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