foo.c: In function 'Primecount':
foo.c:10:3: error: 'flag' undeclared (first use in this function)
   10 |   flag=1;
      |   ^~~~
foo.c:10:3: note: each undeclared identifier is reported only once for each function it appears in
foo.c: In function 'main':
foo.c:29:2: warning: ignoring return value of 'scanf', declared with attribute warn_unused_result [-Wunused-result]
   29 |  scanf("%d %d", &n1, &n2);
      |  ^~~~~~~~~~~~~~~~~~~~~~~~
foo.c:32:3: warning: ignoring return value of 'scanf', declared with attribute warn_unused_result [-Wunused-result]
   32 |   scanf("%d", &a[i]);
      |   ^~~~~~~~~~~~~~~~~~
foo.c:36:3: warning: ignoring return value of 'scanf', declared with attribute warn_unused_result [-Wunused-result]
   36 |   scanf("%d", &b[j]);
      |   ^~~~~~~~~~~~~~~~~~

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