[Tutor] Help with program

[Peter Otten]

Courtney Skinner wrote:

> Hello,
> 
> I am trying to build a program that approximates the value of cosine -
> this is my program so far. It is not returning the right values. Could you
> tell me what I am doing wrong?
> 
> 
> def main():
> 
>     import math
>     
>     print("This program approximates the cosine of x by summing")
>     print("the terms of this series:  x^0 / 0!, -x^2 / 2!,")
>     print("x^4 / 4!, -x^6 / 6!...")
>     
>     n = eval(input("How many terms should be used? "))
>     x = eval(input("What value should be used for x? "))

Consider the more restrictive int() and float() instead of eval().
     
>     s = 1

A nice suggestive name like "sign" instead of "s" might help you with your 
debugging efforts. Of course the same goes for your other names.

>     d = 1
>     e = 1
> 
>     value = 0
>     
>     for i in range(n - 1):
>         value = value + s + (x**e / math.factorial(d))

With the name suggested above the error

         value = value + sign + (x**e / math.factorial(d))

should almost be obvious. sign plus? wait what...

Add
         print("current exponent", e)

to see another problem.

>         
>         s = s * 1

That shows signs of a missing sign ;)

>         e = e + 2
>         d + d + 2
>         
>         
> 
>         print("Approximation for cos(x) calculated by this program: ")
>         print(value)
>         print()
> 
>         difference = math.cos(x) - value
>         
>         print("Difference between this value and math.cos(x): ")
>         print(difference)
> 
> main()
> 
> Thank you!
> 
> C.Skinner