Python Decision Making And Loops.pdf

Python Decision Making
And Loops

Decision making
● Decision making is the most important aspect of almost all the
programming languages.
● Decision structures evaluate multiple logical expressions which produce
TRUE or FALSE as outcome.
● non-zero and non-null values as TRUE, otherwise FALSE

Decision making
Decision making statements in python
1. If
2. If else
3. nested if

Indentation in Python
● For the ease of programming and to achieve simplicity, python doesn't allow
the use of parentheses for the block level code.
● In Python, indentation is used to declare a block.
● If two statements are at the same indentation level, then they are the part of
the same block.
● Generally, four spaces are given to indent the statements which are a typical
amount of indentation in python.

The if statement
The syntax of the if-statement is given below.
if expression:
statement
E.g.
a=10
if a :
print(“ value is ”,a)
or
a=10
if a : print(“ value is ”,a)

The if statement
e.g. X= int(input(“Enter a number”))
r=X%2
if (r==0):
print(“Even”)
print(“Bye”)
o/p:
Enter a number : 3
bye
Enter a number : 50
Even
Bye

The if-else statement
The if-else statement provides an else block combined with the if statement which is
executed in the false case of the condition.
If the condition is true, then the if-block is executed.
Otherwise, the else-block is executed.

Syntax:
if expression:
statement(s)
else :
statement(s)

age = int (input("Enter your age? "))
if age>=18:
print("You are eligible to vote !!");
else:
print("Sorry! You are not eligible to vote !!");

The elif statement
● The elif statement enables us to check multiple conditions and execute the
specific block of statements depending upon the true condition among them.
● We can have any number of elif statements in our program depending upon
our need.
● However, using elif is optional.
● The elif statement works like an if-else-if ladder statement in C. It must be
succeeded by an if statement.

Nested if
• Can use one if or else if statement inside another if or else if statement(s).
• Can have an if...elif...else construct inside another if...elif...else construct.

LOOPS
● Allows us to execute a statement or group of statements multiple times.
1. While loop
2. For loop
3. Nested loop

while loop
● Repeatedly executes target statement(s) as long as a given condition is true
Syntax: while condition:
statement(s)
● Python uses indentation as its method of grouping statements

● In Python, all the statements indented by the same number of character
spaces after a programming construct( if, for , while etc….) are considered to
be part of a single block of code
● While loop needs,
counter variable
condition
increment or decrement
● Infinite loop – Cntl + C

while loop
i=1
number = int(input("Enter the number:"))
while i<=10:
print("%d X %d = %d n" %(number,i,number*i))
i = i+1
Output:
1
2
3
4
5
6
7
8
9
10

While with Else
● Python supports to have an else statement
associated with a loop statement.
● If the else statement is used with a while
loop, the else statement is executed when
the condition becomes false.
●
Print a message once the condition is false:
i = 0
while i < 5:
print("%d is less than 5" %i)
i += 1
else:
print("%d is not less than 5" %i)
Output

Python for loop
The for loop in Python is used to iterate the statements or a part of the program
several times.
It is frequently used to traverse the data structures like list, tuple, or dictionary.
➔ The syntax of for loop in python is given below.
for iterating_var in sequence:
statement(s)

Python for loop
Example-1: Iterating string using for
loop
str = "Python"
for i in str:
print(i)
Output
P
y
t
h
o
n

Python for loop
Program to print the table of the given number .
list = [1,2,3,4,5,6,7,8,9,10]
n = 5
for i in list:
c = n*i
print(c)

For loop Using range() function
The range() function is used to generate the sequence of the numbers.
If we pass the range(10), it will generate the numbers from 0 to 9. The syntax of the
range() function is given below.
Syntax:
range(start,stop,step size)
● The start represents the beginning of the iteration.
● The stop represents that the loop will iterate till stop-1. The range(1,5) will
generate numbers 1 to 4 iterations. It is optional.
● The step size is used to skip the specific numbers from the iteration. It is optional
to use. By default, the step size is 1. It is optional.

Program to print numbers in sequence.
for i in range(10):
print(i,end = ' ')
Output:
0 1 2 3 4 5 6 7 8 9

Program to print table of given number.
n = int(input("Enter the number "))
for i in range(1,11):
c = n*i
print(n,"*",i,"=",c)

Program to print even number using step size in
range().
n = int(input("Enter the number "))
for i in range(2,n,2):
print(i)
Output:
Enter the number 20
2
4
6
8
10
12
14
16
18

Nested for loop in python
Python allows us to nest any number of for loops inside a for loop.
The inner loop is executed n number of times for every iteration of the outer loop.
The syntax is given below.
Syntax
for iterating_var1 in sequence: #outer loop
for iterating_var2 in sequence: #inner loop
#block of statements
#Other statements

Nested for loop in python
# User input for number of rows
rows = int(input("Enter the rows:"))
# Outer loop will print number of rows
for i in range(1,rows+1):
# Inner loop will print number of Astrisk
for j in range(i):
print("*",end = '')
print()
Output:
Enter the rows:5
*
**
***
****
*****

Using else statement with for loop
● Unlike other languages like C, C++, or Java, Python allows us to use the else
statement with the for loop which can be executed only when all the iterations
are exhausted.
● Here, we must notice that if the loop contains any of the break statement then
the else statement will not be executed.

Using else statement with for loop
for i in range(0,5):
print(i)
else:
print("for loop completely exhausted, since there is no break.")
Output :
0
1
2
3
4
for loop completely exhausted, since there is no break.

Python Decision Making And Loops.pdf

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Python Decision Making And Loops.pdf