foo.cc: In function 'int main()':
foo.cc:11:18: warning: comparison of integer expressions of different signedness: 'int' and 'std::__cxx11::basic_string<char>::size_type' {aka 'long unsigned int'} [-Wsign-compare]
   11 |     for(int i=0;i<a1.length();i++) a[i]=a1[i];
      |                 ~^~~~~~~~~~~~
foo.cc:12:18: warning: comparison of integer expressions of different signedness: 'int' and 'std::__cxx11::basic_string<char>::size_type' {aka 'long unsigned int'} [-Wsign-compare]
   12 |     for(int i=0;i<b1.length();i++) b[i]=b1[i];
      |                 ~^~~~~~~~~~~~
foo.cc:13:18: warning: comparison of integer expressions of different signedness: 'int' and 'std::__cxx11::basic_string<char>::size_type' {aka 'long unsigned int'} [-Wsign-compare]
   13 |     for(int i=0;i<c1.length();i++) c[i]=c1[i];
      |                 ~^~~~~~~~~~~~

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