foo.cc: In function 'void solve(char*, char*)':
foo.cc:7:9: error: 'a' was not declared in this scope
  while (a[i]!='\0')
         ^
foo.cc:12:9: error: 'a' was not declared in this scope
  while (a[i]!='\0')
         ^
foo.cc:11:10: warning: unused variable 'k' [-Wunused-variable]
  int j=1,k=1;
          ^
foo.cc: In function 'int main()':
foo.cc:30:10: 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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