foo.cc: In function 'void output(std::vector<int>&)':
foo.cc:4:22: warning: comparison of integer expressions of different signedness: 'int' and 'std::vector<int>::size_type' {aka 'long unsigned int'} [-Wsign-compare]
    4 |         for(int i=0;i<a.size();i++)
      |                     ~^~~~~~~~~
foo.cc: In function 'void merge(std::vector<int>&, std::vector<int>&, std::vector<int>&)':
foo.cc:10:17: warning: comparison of integer expressions of different signedness: 'int' and 'std::vector<int>::size_type' {aka 'long unsigned int'} [-Wsign-compare]
   10 |          while(i<a.size()&&j<b.size()){
      |                ~^~~~~~~~~
foo.cc:10:29: warning: comparison of integer expressions of different signedness: 'int' and 'std::vector<int>::size_type' {aka 'long unsigned int'} [-Wsign-compare]
   10 |          while(i<a.size()&&j<b.size()){
      |                            ~^~~~~~~~~
foo.cc:18:17: warning: comparison of integer expressions of different signedness: 'int' and 'std::vector<int>::size_type' {aka 'long unsigned int'} [-Wsign-compare]
   18 |          while(i<a.size()){
      |                ~^~~~~~~~~
foo.cc:21:17: warning: comparison of integer expressions of different signedness: 'int' and 'std::vector<int>::size_type' {aka 'long unsigned int'} [-Wsign-compare]
   21 |          while(j<b.size()){
      |                ~^~~~~~~~~

[Hydro](https://hydro.ac)提供评测服务