# FOR LOOPS

# this for loop starts at 0, stops at 5-1
for i in range(5):
  print(i)

print()  # print a blank line

# iterate letters in a text string
# first time through the loop the variable 'letter' is d, then o, then g
# letter is just a variable name. we can change it to whatever we want
for letter in "dog":
  print(letter)

print()

# loop starts with 5 and continues to 10-1
for i in range(5, 10):
  print (i**2)  # print i squared

print()

# parameters for the range function: (start, stop-1, step)
# in this loop, start=10, end=20-1, step=3 
# (every third number from 10 to 19)
for i in range(10, 20, 3):
  print(i)

print()

# for loop iterates a list
# here the list is a list of text strings, bird names
# birds is our variable name for the list
# i is our variable name for each bird in the list inside the for loop.
birds = ['robin', 'sparrow', 'duck']
for i in birds:
  print(len(i))  # print number of letters in each item