Practice
p
The mathematical constant p may be calculated using the series formula
p = 4 ( 1  1/3 + 1/5  1/7 + ... )

Write a function with the header
that receives as a parameter the number of terms to be used in calculating
the approximate value of p and returns that value.
The mathematical constant p may also be calculated using the Wallis product
p = 2 [ (2/1) * (2/3) * (4/3) * (4/5) * (6/5) * (6/7) ... ]

Write a second function with the header
double pi_wallis ( int nterms )

that receives as a parameter the number of terms to be used in calculating the approximate value of
p and returns that value.
Finally, write a main program that evaluates p for an increasing number of terms
and displays the results returned from both functions so as to show the relative rate of convergence
of each method of approximation.
