exercises

1. Write a program to take the sum of all integers from 2 to 17 excluding 13.
2. The Fibonacci sequence is a sequence of numbers that proceeds as follows: 0, 1, 1, 2, 3, 5, 8, 13, 21, etc. Each number is the sum of the previous two. We can write a function to compute a number in this sequence using Python:

   file: fib.py
   1	def fib(n):
   2	if n == 0:
   3	return 0
   4	elif n == 1:
   5	return 1
   6	return fib(n-1)+fib(n-2)
   7
   8	print fib(7)
   > python fib.py 13

   When a function calls itself (the way fib() does) it is called recursion. Use recursion to write a program to compute a factorial (4! = 4*3! = 4*3*2*1, and 1!=1)
3. Write a program to make a copy of an array with the even integers removed. You can test for whether a number is even by using the % operator.

   file: remain.py
   1	import random
   2
   3	# create a list of 10 random integers from 1 to 100
   4	# define a function that returns a new array that is
   5	# the same as your randomly generated one, except that
   6	# the even numbers are removed.
   7	a = []
   8	for i in range(10):
   9	a.append(random.randint(1,100))
   10	print a
   11
   12	# Here's how you calculate remainders:
   13	print "remainder of 15 / 2 =",15 % 2
   14	print "remainder of 39 / 3 =",39 % 3
   > python remain.py [45, 88, 42, 43, 74, 20, 42, 93, 72, 26] remainder of 15 / 2 = 1 remainder of 39 / 3 = 0

4. Write a program to convert a decimal number to an array of digits. In other words, make a function that converts 1298 to [1,2,9,8].
5. Write a program to convert an array of digits to a number. In other words, one that converts [3,9,5,2] to 3952.
6. Write a program to convert an array of decimal digits to octal digits.
7. Write a program to convert an array of octal digits to decimal digits.
8. Write a program to compute the answer to the quadratic formula. In other words, create a function that takes three values: a,b, and c, and returns the two solutions of a*x**2+b*x+c==0.
9. Write a program to determine whether a number is a perfect square. The program should print "true" if it is a perfect square and "false" otherwise.
10. Using the fact that string is an array of characters, write a find() program that works like string's find method.
11. Write a program to sort an array. First, create a random array as follows:

    file: sort.py
    1	import random
    2
    3	a = []
    4	for i in range(10):
    5	a.append(random.randint(1,100))
    6	print a
    7
    8	# put code here that sorts array a
    > python sort.py [5, 83, 74, 11, 9, 11, 50, 59, 85, 22]