[Tutor] Help with program

[Mark Lawrence]

On 16/02/2015 16:27, 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

Not that it matters but imports are usually done at the top of the module.

>
>      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? "))

*DON'T* use eval, it's potentially dangerous.

n = int(input("How many terms should be used? "))
x = float(input("What value should be used for x? "))

>
>      s = 1
>      d = 1
>      e = 1
>
>      value = 0
>
>      for i in range(n - 1):

Are you aware that this will count from zero to n - 2?

>          value = value + s + (x**e / math.factorial(d))
>
>          s = s * 1
>          e = e + 2
>          d + d + 2

Whoops :)

>          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()

We'd usually write:-

if __name__ == "__main__":
     main()

>
> Thank you!
>
> C.Skinner

-- 
My fellow Pythonistas, ask not what our language can do for you, ask
what you can do for our language.

Mark Lawrence