Control Flow - While Loops
The while statement iterates (repeats) the same code block as long as certain condition is met. Iteration means executing the same block of code over and over. A code that implements iteration is called a loop. Python has two primitive loop commands:
| while loops | Indefinite iteration | The number of times the loop is executed isn’t specified explicitly in advance |
|---|---|---|
| for loops | Definite iteration | The number of times the designated block will be executed is specified explicitly at the time the loop starts |
Before every iteration the while condition is calculated. If True - the block beneath the command is executed.
Here is an example:
#while
x = 1
while x < 5:
print(x)
x += 1
print("loop ended")
Here is a diagram describing the process:
The continue Statement
Using the continue statement we can skip the current iteration, and continue to the next one:
#continue
x = 0
while x < 5:
x += 1
if x == 3:
continue
print(x)
The break Statement
Using the break statement we can exit the loop (not just one iteration):
#break
x = 1
while x < 5:
if x == 3:
break
print(x)
x += 1
The else Statement
Using the else statement we can run code when the condition is False:
#else
x = 1
while x < 5:
print(x)
x += 1
else:
print('While loop is a great tool')
Nested while Statements
It is possible to use a nested while statement:
#nested while
x = 1
while x < 10:
print(x)
while x < 3:
print("We are at the very beginning")
x += 1
else:
print('While loop is a great tool')
Exercise
- Define a variable with the value of 2.
- Create a while loop that runs as long value equals less than 20.
- Inside the loop print the variable and add 2 to the variable.
#Write your code here: