foo.cc: In member function 'BigInt BigInt::operator+(const BigInt&) const':
foo.cc:76:7: warning: unused variable 'carry' [-Wunused-variable]
   76 |   int carry = 0;
      |       ^~~~~
foo.cc: In member function 'BigInt BigInt::operator=(const char*)':
foo.cc:117:10: error: 'strlen' was not declared in this scope
  117 |   size = strlen(num);
      |          ^~~~~~
foo.cc:3:1: note: 'strlen' is defined in header '<cstring>'; did you forget to '#include <cstring>'?
    2 |  #include<vector>
  +++ |+#include <cstring>
    3 | #include<string>

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