Control flow statements

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

Conditional loops with while

Exercise

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

While loops combine for and if. They require a conditional expression at the beginning. The conditional expressions work in exactly the same way as in if.. elif statements.

i = 0
while i < 5:
    print (i)
    i = i + 1)

When to use while?

When there is an exit condition.
When it may happen that nothing is done at all.
When the number of repeats depends on user input.
Searching for a particular element in a list.

Exercises

Exercise 1

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 2

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 3

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 4

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))