/in/foo.cc: In function 'int ysh(int)':
/in/foo.cc:10:9: warning: 'sum' may be used uninitialized in this function [-Wmaybe-uninitialized]
  return sum;
         ^~~
/in/foo.cc: In function 'int main()':
/in/foo.cc:18:16: warning: 'sum' may be used uninitialized in this function [-Wmaybe-uninitialized]
    if(ysh(i)==j&&ysh(j)==i&&i<j)
       ~~~~~~~~~^~~~~~~~~~~
/in/foo.cc:18:27: warning: 'sum' may be used uninitialized in this function [-Wmaybe-uninitialized]
    if(ysh(i)==j&&ysh(j)==i&&i<j)
       ~~~~~~~~~~~~~~~~~~~~^~~~~