Problem
The mean of a sequence of numbers is their sum divided by the count of numbers in the sequence. The (population) variance of the sequence is the mean statistics of the squares of all numbers in the sequence, minus the square of the mean of the numbers in the sequence. The standard deviation is the square root of the variance. Write a well-structured C++ function to calculate the standard deviation of a sequence of n floating-point numbers, where n is a constant and the numbers are in an array indexed from 0 to n - 1, which is a parameter to the function. Use, then write, subsidiary functions to calculate the mean and variance.