foo.cc: In function 'int main()':
foo.cc:8:15: warning: comparison of integer expressions of different signedness: 'int' and 'std::__cxx11::basic_string<char>::size_type' {aka 'long unsigned int'} [-Wsign-compare]
    8 |  for(int i=0;i<st.size()-1;i++)
      |              ~^~~~~~~~~~~~
foo.cc:12:12: warning: suggest parentheses around '&&' within '||' [-Wparentheses]
   12 |  if(sum==10&&st[st.size()-1]=='X'||sum<10&&st[st.size()-1]==sum+'0')
      |     ~~~~~~~^~~~~~~~~~~~~~~~~~~~~~

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