/in/foo.cc: In function 'int main()':
/in/foo.cc:9:18: error: 'itoa' was not declared in this scope
  itoa (j, str, 10); //j为int，str为char 
                  ^
/in/foo.cc:10:12: warning: comparison with string literal results in unspecified behavior [-Waddress]
  if(str == "X"){
            ^~~
/in/foo.cc:25:6: error: expected ';' before 'j'
   j  j=sum%11;
      ^
/in/foo.cc:25:14: warning: statement has no effect [-Wunused-value]
   j  j=sum%11;
              ^