foo.cc: In function 'int main()':
foo.cc:15:15: warning: comparison between signed and unsigned integer expressions [-Wsign-compare]
  for(int i=0;i<n.size();i++)
              ~^~~~~~~~~
foo.cc:19:2: warning: this 'while' clause does not guard... [-Wmisleading-indentation]
  while((a[l]=getchar())!='\n') l++;l--; 
  ^~~~~
foo.cc:19:36: note: ...this statement, but the latter is misleadingly indented as if it were guarded by the 'while'
  while((a[l]=getchar())!='\n') l++;l--; 
                                    ^
foo.cc:17:7: warning: ignoring return value of 'int scanf(const char*, ...)', declared with attribute warn_unused_result [-Wunused-result]
  scanf("%c",&a[0]);
  ~~~~~^~~~~~~~~~~~

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