foo.cc: In function 'int main()':
foo.cc:11:11: warning: statement has no effect [-Wunused-value]
    sum+sum+i;
    ~~~~~~~^~
foo.cc:8:10: warning: 'm' is used uninitialized in this function [-Wuninitialized]
  for(int i=m;i<=n;i++)
          ^
foo.cc:8:15: warning: 'n' is used uninitialized in this function [-Wuninitialized]
  for(int i=m;i<=n;i++)
              ~^~~

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