Check out example codes for "what is difffrence between s.length() and s.size()". It will help you in understanding the concepts better.

Code Example 1

The size() function is consistent with other STL containers 
(like vector, map, etc.) and length() is consistent with most 
peoples intuitive notion of character strings like a word, sentence
or paragraph. We say a paragraph'ss length not its size, so length() 
is to make things more readable.

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