foo.cc: In function 'char* quling(char*, char*)':
foo.cc:14:8: warning: statement has no effect [-Wunused-value]
   for(x;x<y;x++){
        ^
foo.cc: In function 'int cmp(char*, char*, char*, char*)':
foo.cc:36:10: warning: statement has no effect [-Wunused-value]
    for(a1;a1<b1;a1++,a2++){
          ^
foo.cc: In function 'int main()':
foo.cc:71:7: warning: ignoring return value of 'int scanf(const char*, ...)', declared with attribute warn_unused_result [-Wunused-result]
  scanf("%s",str);
  ~~~~~^~~~~~~~~~