C++ arithmetic problems, about strings, shaping, for statements and switch statements.
The condition *p in for is equivalent to *p! =0, indicating that P is not pointing to 0 at present, indicating the end of the string.
The whole loop is used to count the number of various characters in the string S. v 1 stands for' a', that is, 1, v2 stands for' b', that is, 2, and v3 stands for' e', that is, 5.