foo.cc: In function 'int main()':
foo.cc:15:2: error: 'scanf' was not declared in this scope
   15 |  scanf("%d",&n);
      |  ^~~~~
foo.cc:19:2: error: 'printf' was not declared in this scope
   19 |  printf("%d\n",count);
      |  ^~~~~~
foo.cc:1:1: note: 'printf' is defined in header '<cstdio>'; did you forget to '#include <cstdio>'?
  +++ |+#include <cstdio>
    1 | int isPrime(int x)

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