Computer Science
Class -XI
Code No. 083
2023-24




CLASS-XI
SUBJECT: COMPUTER SCIENCE (083) – PYTHON
INDEX
NO. CHAPTER NAME 
1 INTRODUCTION TO PYTHON 
2 PYTHON FUNDAMENTALS 
3 DATA HANDLING 
4 FLOW OF CONTROL 






CHAPTER-4
FLOW OF CONTROL
1. Decision Making and branching (Conditional Statement)
2. Looping or Iteration
3. Jumping statements
4.1 DECISION MAKING & BRANCHING
Decision making is about deciding the order of execution 
of statements based on certain
conditions. Decision structures evaluate multiple 
expressions which produce TRUE or FALSE
as outcome.
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There are three types of conditions in python:
1. if statement
2. if-else statement
3. elif statement
1. if statement: It is a simple if statement. When 
condition is true, then code which is
associated with if statement will execute.
Example:
a=40
b=20
if a>b:
print(“a is greater than b”)
2. if-else statement: When the condition is true, 
then code associated with if statement will
execute, otherwise code associated with else 
statement will execute.
Example:
a=10
b=20
if a>b:
print(“a is greater”)
else:
print(“b is greater”)
3. elif statement: It is short form of else-if 
statement. If the previous conditions were not true,
then do this condition". It is also known as 
nested if statement.
Example:
a=input(“Enter first number”)
b=input("Enter Second Number:")
if a>b:
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print("a is greater")
elif a==b:
print("both numbers are equal")
else:
print("b is greater")
4.2 LOOPS in PYTHON
Loop: Execute a set of statements repeatedly until 
a particular condition is satisfied.
There are two types of loops in python:
1. while loop
2. for loop
Loops in
Python
while
loop
for loop
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1. while loop: With the while loop we can execute 
a set of statements as long as a condition is
true. It requires to define an indexing variable.
Example: To print table of number 2
i=2
while i<=20:
print(i)
i+=2
2. for loop : The for loop iterate over a given 
sequence (it may be list, tuple or string).
Note: The for loop does not require an indexing 
variable to set beforehand, as the for command
itself allows for this.
primes = [2, 3, 5, 7]
for x in primes:
print(x)
The range( ) function:
it generates a list of numbers, which is generally 
used to iterate over with for loop.
range( ) function uses three types of parameters, 
which are:
 start: Starting number of the sequence.
 stop: Generate numbers up to, but not including 
last number.
 step: Difference between each number in the 
sequence.
Python use range( ) function in three ways:
a. range(stop)
b. range(start, stop)
c. range(start, stop, step)
Note:
 All parameters must be integers.
 All parameters can be positive or negative.
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a. range(stop): By default, It starts from 0 and 
increments by 1 and ends up to stop,
but not including stop value.
Example:
for x in range(4):
print(x)
Output:
0
1
2
3
b. range(start, stop): It starts from the start value 
and up to stop, but not including
stop value.
Example:
for x in range(2, 6):
print(x)
Output:
2
3
4
5
c. range(start, stop, step): Third parameter specifies 
to increment or decrement the value by
adding or subtracting the value.
Example:
for x in range(3, 8, 2):
print(x)
Output:
3
5
7
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Explanation of output: 3 is starting value, 8 is stop 
value and 2 is step value. First print 3 and
increase it by 2, that is 5, again increase is by 2, 
that is 7. The output can’t exceed stop-1 value
that is 8 here. So, the output is 3, 5, 8.
Difference between range( ) and xrange( ):
S.
No. range( ) xrange( )
1 returns the list of numbers returns the generator 
object that can be used
to display numbers only by looping
2 The variable storing the range takes more
memory variable storing the range takes less memory
3 all the operations that can be applied on
the list can be used on it
operations associated to list cannot be
applied on it
4 slow implementation faster implementation
4.3 JUMP STATEMENTS:
There are two jump statements in python:
1. break
2. continue
1. break statement : With the break statement we can 
stop the loop even if it is true.
Example:
in while loop in for loop
i = 1
while i < 6:
print(i)
if i == 3:
break
i += 1
languages = ["java", "python", "c++"]
for x in languages:
if x == "python":
break
print(x)
Output:
1
2
3
Output:
java
Note: If the break statement appears in a nested loop, 
then it will terminate the very loop it is
in i.e. if the break statement is inside the inner loop 
then it will terminate the inner loop only
and the outer loop will continue as it is.
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2. continue statement : With the continue statement 
we can stop the current iteration, and
continue with the next iteration.
Example:
in while loop in for loop
i = 0
while i < 6:
i += 1
if i == 3:
continue
print(i)
languages = ["java", "python", "c++"]
for x in languages:
if x == "python":
continue
print(x)
Output:
1
2
4
5
6
Output:
java
c++
4.4 Loop else statement:
The else statement of a python loop executes when 
the loop terminates normally. The else
statement of the loop will not execute when the 
break statement terminates the loop.
The else clause of a loop appears at the same 
indentation as that of the loop keyword while or
for.
Syntax:
for loop while loop
for  in :
statement-1
statement-2
.
.
else:
statement(s)
while :
statement-1
statement-2
.
.
else:
statement(s)
4.5 Nested Loop :
A loop inside another loop is known as nested loop.
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3. Write a program to check a year whether it is leap 
year or not.
year=int(input("Enter the year: "))
if year%100==0 and year%400==0:
print("It is a leap year")
elif year%4==0:
print("It is a leap year")
else:
print("It is not leap year")
4. Write a program in python to convert °C to °F
and vice versa.
a=int(input("Press 1 for C to F \n Press 2 for F to C \n"))
if a==1:
c=float(input("Enter the temperature in degree celcius: "))
f= (9/5)*c+32
print(c, "Celcius = ",f," Fahrenheit")
elif a==2:
f=float(input("Enter the temperature in Fahrenheit: "))
c= (f-32)*5/9
print(f, "Fahrenheit = ",c," Celcius")
else:
print("You entered wrong choice")
5. Write a program to check a number whether it is 
palindrome or not.
num=int(input("Enter a number : "))
n=num
res=0
while num>0:
rem=num%10
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res=rem+res*10
num=num//10
if res==n:
print("Number is Palindrome")
else:
print("Number is not Palindrome")
6. A number is Armstrong number or not.
num=input("Enter a number : ")
length=len(num)
n=int(num)
num=n
sum=0
while n>0:
rem=n%10
sum=sum+rem**length
n=n//10
if num==sum:
print(num, "is armstrong number")
else:
print(num, "is not armstrong number")
7. To check whether the number is perfect number or not
num=int(input("Enter a number : "))
sum=0
for i in range(1,num):
if(num%i==0):
sum=sum+i
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if num==sum:
print(num, "is perfect number")
else:
print(num, "is not perfect number")
8. Write a program to print Fibonacci series.
n=int(input("How many numbers : "))
first=0
second=1
i=3
print(first, second, end=" ")
while i<=n:
third=first+second
print(third, end=" ")
first=second
second=third
i=i+1
9. To print a pattern using nested loops
for i in range(1,5):
for j in range(1,i+1):
print(j," ", end=" ")
print('\n')
1
1 2
1 2 3
1 2 3 4
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