This document provides an overview of Python decision control statements, including if, if-else, nested if-else, and if-elif statements. It explains the functionality of each type of statement with examples that demonstrate how to execute code based on specific conditions. Additionally, it contains sample programs to check numerical conditions such as positivity, even/odd status, and grade assessment based on input scores.

1. BCS-DS-427B: PYTHON
Manav Rachna International Institute of Research and Studies, Faridabad

2. PYTHON
Decision Control Statements
ADITI Gaur
Associate Professor, CSE
MRIIRS
BCS-DS-427B: PYTHON

3. Decision Control/Conditional
Statements
Logical
Allows us to execute a set of code based on some
condition
Types
● If statement
● If..else statement
● Nested-if-else
● If-elif
If (Ghost is there)
do nothing
If(Ghost is there)
say “AHHHH!!”
Source - https://img.devrant.com/devrant/rant/r_1647754_X1Twj.jpg

4. Conditional Statements
Nested-if-else
If-else
If condition is true
code1 is exceuted ,
else code2 is
exceuted
When one if –else is
present within another if-
else and used to check
multiple conditions
If-elif
Allows you to check multiple
conditions and execute a
block of code whose
condition evaluates to TRUE
if(condition):
code1
else:
code2
if(condition1):
code1
elif(condition2):
code2
else:
code3
if(condition1):
code1
else:
if(condition2):
code2
else:
code3

5. If Decision Control Statement
• The if decision control flow statement starts with if keyword and ends
with a colon.
• The if statement decides whether to run some particular statement or
not depending upon the value of the Boolean expression.
• If the Boolean expression evaluates to True then statements in the if
block will be executed; otherwise the result is False then none of the
statements are executed.
• In Python, the if block statements are determined through indentation
and the first unindented statement marks the end.

6. ● Program Reads a Number and Prints a Message If It Is Positive
number = int(input("Enter a number"))
if number >= 0:
print("The number entered by the user is a positive number")
Output
Enter a number 6
The number entered by the user is a positive number
● Program to Read Luggage Weight and Charge the Tax Accordingly
weight = int(input("How many pounds does your suitcase weigh?"))
if weight > 50:
print("There is a $25 surcharge for heavy luggage")
print("Thank you")

7. if…else Decision control statement
● if…else statement allows for a two-way decision.

8. ● Program to Find If a Given Number Is Odd or Even
number = int(input("Enter a number"))
if number % 2 == 0:
print(f"{number} is Even number")
else:
print(f"{number} is Odd number“
Output
Enter a number: 45
45 is Odd number

9. Program to Check If a Given Year Is a Leap Year
year=int(input("Enter year to be checked:"))
if(year%4==0 and year%100!=0 or year%400==0):
print("The year is a leap year!")
else:
print("The year isn't a leap year!")

10. Nested-if-else statement

11. Program to Check If a Number is +ve,-ve or
zero using nested if else
num=int(input("Enter a number"))
if(num>0):
print(“Number is positive”)
else:
if(num<0):
print(“Number is negative”)
else:
print(“Number is zero”)

12. ● The if…elif…else is also called as multi-way decision control
statement.
if…elif…else Statement

13. Program to Check If a Number is +ve,-ve or
zero using if-elif-else
num=int(input("Enter a number"))
if(num>0):
print(“Number is positive”)
elif(num<0):
print(“Number is negative”)
else:
print(“Number is zero”)

14. Write a Program to Prompt for a Score between 0.0 and 1.0. If the Score Is
Out of Range, Print an Error. If the Score Is between 0.0 and 1.0, Print a
Grade Using the Following Table

15. Solution
score = float(input("Enter your score"))
if score < 0 or score > 1:
print('Wrong Input')
elif score >= 0.9:
print('Your Grade is "A" ')
elif score >= 0.8:
print('Your Grade is "B" ')
elif score >= 0.7:
print('Your Grade is "C" ')
elif score >= 0.6:
print('Your Grade is "D" ')
else:
print('Your Grade is "F" ')
Output
Enter your score0.92
Your Grade is "A"

16. Write program to :
a) find person is eligible to vote or not using if-
else
b) Determine triangle is equilateral or isoceles
c) Find roots of quadratic equation are real or
imaginary or zero