foo.cc: In function 'int fac(int)':
foo.cc:21:1: warning: control reaches end of non-void function [-Wreturn-type]
 }
 ^
foo.cc: In function 'int main()':
foo.cc:32:20: warning: 'n1' is used uninitialized in this function [-Wuninitialized]
  cout<<n<<"="<<n1<<"+"<<n2;
                    ^~~
foo.cc:32:23: warning: 'n2' is used uninitialized in this function [-Wuninitialized]
  cout<<n<<"="<<n1<<"+"<<n2;
  ~~~~~~~~~~~~~~~~~~~~~^~~~

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