/in/foo.cc: In function 'int main()':
/in/foo.cc:13:14: warning: comparison between signed and unsigned integer expressions [-Wsign-compare]
     for(i=0;i<str1.size();i++) // str1.size()返回str1中字符个数 
             ~^~~~~~~~~~~~
/in/foo.cc:19:22: warning: suggest parentheses around '&&' within '||' [-Wparentheses]
             if(s>'Z' && s<'a' || s>'z')
                ~~~~~~^~~~~~~~