foo.cc: In function 'int main()':
foo.cc:24:17: warning: format '%s' expects argument of type 'char*', but argument 2 has type 'int' [-Wformat=]
     scanf("%s",s);           //s为要处理的加密字符串，答案储存在ans里
                 ^
foo.cc:25:12: error: could not convert 's' from 'char' to 'std::__cxx11::string {aka std::__cxx11::basic_string<char>}'
     solve(s);
            ^
foo.cc:23:7: warning: unused variable 'ans' [-Wunused-variable]
  char ans;
       ^~~
foo.cc:24:10: warning: ignoring return value of 'int scanf(const char*, ...)', declared with attribute warn_unused_result [-Wunused-result]
     scanf("%s",s);           //s为要处理的加密字符串，答案储存在ans里
     ~~~~~^~~~~~~~

[Hydro](https://hydro.ac)提供评测服务