foo.cc: In function 'int main()':
foo.cc:10:29: error: 'strlen' was not declared in this scope
   10 |         for (int i = 0; i < strlen(a); i++)
      |                             ^~~~~~
foo.cc:3:1: note: 'strlen' is defined in header '<cstring>'; did you forget to '#include <cstring>'?
    2 | #include<cmath>
  +++ |+#include <cstring>
    3 | using namespace std;
foo.cc:13:29: error: 'strlen' was not declared in this scope
   13 |         for (int i = 0; i < strlen(a); i++)
      |                             ^~~~~~
foo.cc:13:29: note: 'strlen' is defined in header '<cstring>'; did you forget to '#include <cstring>'?
foo.cc:24:29: error: 'strlen' was not declared in this scope
   24 |         for (int i = 0; i < strlen(a) - 1; i++)
      |                             ^~~~~~
foo.cc:24:29: note: 'strlen' is defined in header '<cstring>'; did you forget to '#include <cstring>'?

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