Loops in python programming

1. Loops in python
programming
➔ For
➔ while

2. Outline
1. For loop
2. Range function
3. Break, continue, and Pass
statement
4. Booleans
5. While loop
6. Nested loop

3. For Loop
The for loop in python iterates over the items of any sequence
be it a list or a string. Moreover, using for loop in the program
will minimize the line of code.
Points to keep in mind while using for loop in python:
➔ It should always start with for keyword and should
end with a colon(:).
➔ The statements inside the loop should be
indented(four spacebars).
Syntax:
For iterator_variable in sequence:
statement(s)

4. Example
Code:
for i in range(6):
print(“Hello World!”)
Output:
print(“Hello World!”)
print(“Hello World!”)
print(“Hello World!”)
print(“Hello World!”)
print(“Hello World!”)
This is actually a temporary
variable which store the
number of iteration
Number of times you want to
execute the statement

5. Range function
To iterate over a sequence of numbers, the built-in function
range() comes in handy. It generates arithmetic
progressions. For example, if we want to print a whole number
from 0 to 10, it can be done using a range(11) function in a for
loop.
In a range() function we can also define an optional start and
the endpoint to the sequence. The start is always included
while the endpoint is always excluded.
Example:
for i in range(1, 6):
print("Hello World!")
Output: Prints Hello World! five times
Starting point
Ending point

6. Range function
The range() function also takes in another optional
parameter i.e. step size. Passing step size in a range()
function is important when you want to print the value
uniformly with a certain interval.
Step size is always passed as a third parameter where the
first parameter is the starting point and the second
parameter is the ending point. And if the step_size is not
provided it will take 1 as a default step_size.
Example:
for i in range(0,20, 2):
print(i)
Output: prints all the even numbers till 20
Step size
cont….

7. Sum of numbers
-Write a program to find the sum of all the numbers less than
a number entered by the user. Display the sum.
Expected Output:
1

8. Break, Continue, & Pass Statement
(Loop control statement)
➔ A break statement is used to immediately terminate a
loop.
➔ A continue statement is used to skip out future
commands inside a loop and return to the top of the
loop.
➔ A Pass is a null operation — when it is executed,
nothing happens. It is useful as a placeholder when a
statement is required syntactically when no code
needs to be executed.
➔ These statements can be used with for or while loops.

9. Break, Continue, & Pass Statement (Loop control statement)
Example:
for i in range(10):
if i == 3:
break
print(i)
Output:
0
1
2
Break
for i in range(5):
if i == 3:
continue
print(i)
Output:
0
1
2
4
Continue
for i in range(10):
Pass
Output:
Nothing will be printed
Pass

10. Magic Number
Write a program that makes the user guess a particular
number between 1 and 100. Save the number to be
guessed in a variable called magic_number.
If the user guesses a number higher than the secret
number, you should say Too high!. Similarly, you should
say Too low! if they guess a number lower than the secret
number. Once they guess the number, say Correct!
Expected Output:
2

11. Boolean
A boolean is a value that can be either True or False.
Example:
brought_food = True
brought_drink = False
- Boolean variables don't have quotation marks.
- The values must start with capital letters.

12. While Loop
➔ while loop repeatedly carries out a target statement while the condition is
true. The loop iterates as long as the defined condition is True.
➔ When the condition becomes false, program control passes to the line
immediately following the loop.
Example:
while True:
print("I am a programmer")
break
while False:
print("Not printed because while the condition is already False")
break
Output:
I am a programmer

13. While Loop
Example:
x = 1
while x > 0:
print ("Hello!")
x = x - 1
print ("I like Python.")
Output:
Hello!
I like Python.

14. Guess the number
Write a program where the user enters a number.
If the number matches the number, acknowledge
the user and stop the program. If the number
does not match, keep asking for the next number.
Expected Output:
3

15. Nested Loop
Loop within a loop is called a nested loop.
➔ For loop within for loop is called a nested for loop.
➔ While loop within while loop is called as nested while
loop.
for i in range(4):
for j in range(3):
print ("Hello!")
Example: Nested for loop
i = 1
j = 5
while i < 4:
while j < 8:
print(i,",", j)
j = j + 1 j
i = i + 1
Example: Nested while loop

16. Nested Loop(Example)
for i in range(4):
x = 5
while x > 1:
print (x)
x = x - 1
Output:
5
4
3
2
5
4
3
2
5
4
3
2
5
4
3
2

17. Rolling a dice
Write a program that will print out all combinations that can
be made when 2 dice are rolled. And should continue until all
values up to 6, and 6 are printed. (Hint: You should have a
space after each comma!)
Expected Output:
4

18. Multiplication Table:
Write a program to print a multiplication
table to 12 of a given number.
Expected Output:
1

19. Printing pattern:
Write a program to print the following two
patterns implementing the nested loop
concept.
2