foo.cc: In function 'void solve(char*, char*)':
foo.cc:19:5: warning: converting to non-pointer type 'char' from NULL [-Wconversion-null]
  *p=NULL;
     ^~~~
foo.cc: In function 'int main()':
foo.cc:27:10: 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
     ~~~~~^~~~~~~~

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