foo.cc: In function 'int fn(int)':
foo.cc:9:6: warning: unused variable 'f' [-Wunused-variable]
  int f;
      ^
foo.cc: In function 'int main()':
foo.cc:22:6: warning: unused variable 'i' [-Wunused-variable]
  int i,j,m,n2,a=0;
      ^
foo.cc:22:8: warning: unused variable 'j' [-Wunused-variable]
  int i,j,m,n2,a=0;
        ^
foo.cc:22:10: warning: unused variable 'm' [-Wunused-variable]
  int i,j,m,n2,a=0;
          ^
foo.cc: In function 'int fn(int)':
foo.cc:18:1: warning: control reaches end of non-void function [-Wreturn-type]
 }
 ^

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