Remarks:
Operation of the String class
Some containers STL operation: stack, map, vector
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link:
C ++ string class string explain common operations (a) INITIALIZE traverse connecting]: https://www.cnblogs.com/qiumingcheng/p/7872545.html
C ++ Standard Template Library STL's Stack: https://www.cnblogs.com/drq1/p/9699475.html