/in/foo.cc: In function 'int main()':
/in/foo.cc:8:11: warning: comparison between signed and unsigned integer expressions [-Wsign-compare]
  for(i++;i<strlen(f);i++)c=c*10+(f[i]-48);//等号右边的数 
          ~^~~~~~~~~~
/in/foo.cc:9:15: warning: comparison between signed and unsigned integer expressions [-Wsign-compare]
  for(int m=1;m<strlen(ab);m++){//m前为a,后为b 
              ~^~~~~~~~~~~
/in/foo.cc:12:9: warning: comparison between signed and unsigned integer expressions [-Wsign-compare]
   for(;n<strlen(ab);n++)b=b*10+(ab[n]-48);
        ~^~~~~~~~~~~