while.md

Conditional loops with while

Control flow means controlling, which instruction is handled next. In this tutorial, we cover three of Pythons control flow statements: for, if and while.

Exercise 1

Match the expressions so that the while loops run the designated number of times.

Exercise 2

Which of these while commands are correct?

• while a = 1:
• while b == 1
• while a + 7:
• while len(c) > 10:
• while a and (b-2 == c):
• while s.find('c') >= 0:

Exercise 3

Which statements are correct?

• while is also called a conditional loop
• The expression after while may contain function calls
• It is possible to write endless while loops
• The colon after while may be omitted
• The code block after while is executed at least once

Exercise 4

The following for loop searches for 33 in the data. Change the code so that it uses a while loop instead.

data = [5, 7, 33, 12, 4, 3, 18]

found = False
for n in data:
    if n == 33:
        found = True

print("The value 33 has been found: {}".format(found))

Exercise 5

The following while loop counts numbers higher than 10. Change the code so that it uses a for loop instead.

data = [4, 7, 11, 1, 3,  15]

i, j = 0,0
while i < len(data):
    if data[i] > 10:
        j += 1
    i += 1

print("Values higher than 10: {}".format(j))

Exercise 6

Will the following while loop finish?

count = 0
while count > 0:
    print count
    count += 1

Exercise 6

Will the following while loop finish?

text = "a"
while "z" not in text:
    text += "a"

Exercise 7

Will the following while loop finish? than a = 7 b = 135 while a != b: a += (a - b) / 10.0 b -= (a - b) / 10.0

Exercise 8

Will the following while loop finish?

n = 0
while n * 5 != n ** 2:
    n += 2

Exercise 9

Will the following while loop finish?

data = [1,2,7,8]
while data[-1] > 2:
    data.pop()

Exercise 10

Will the following while loop finish?

data = [2,3,15]
while data[0] < 100:
    data = data[1:]