UNIT – II

Control Statements: Selection/Conditional Branching statements: if, if-else, nested if

and if-elif-else statements. Iterative Statements: while loop, for loop, else suite in
loop and nested loops. Jump Statements: break, continue and pass statements.

Control Statements
In any programming language a program may execute sequentially, selectively or
iteratively. Every programming language provides constructs to support Sequence,
Selection and Iteration. In Python all this construct can broadly categorized in 2 categories.
A. Conditional Control Construct
(Selection, Iteration)
B. Un- Conditional Control Construct
(pass, break, continue, exit(), quit())
Python have following types of control statements
1. Selection ( branching) Statement Conditional
2. Iteration ( looping) Statement
3. Jumping (break / continue)Statement
Un Conditional Control
Statements
Python Selection Statements

Python have following types of selection statements

1. if statement
2. if else statement
3. Ladder if else statement (if-elif-else)
4. Nested if statement

Python If statements
This construct of python program consist of one if condition with one block of
statements. When condition becomes true then executes the block given below it.
Syntax:
if ( condition):
…………………..
…………………..
Flow Chart: it is a graphical representation of steps an algorithm to solve a problem.
Example:
Age=int(input(“Enter Age: “))
If ( age>=18):
Print(“You are eligible for vote”)
If(age<0):
Print(“You entered Negative Number”)
Python if - else statements
This construct of python program consist of one if condition with two blocks. When
condition becomes true then executes the block given below it. If condition evaluates result
as false, it will executes the block given below else.
Syntax:
if ( condition):
…………………..

else:
…………………..
…………………..
Flowchart
Example-1:
Age=int(input(“Enter Age: “))
if ( age>=18):
print(“You are eligible for vote”)
else:
print(“You are not eligible for vote”)
Example-2:
N=int(input(“Enter Number: “))
if(n%2==0):
print(N,“ is Even Number”)
Else:
print(N,“ is Odd Number”)

Python Ladder if else statements (if-elif-else)

This construct of python program consist of more than one if condition. When first
condition evaluates result as true then executes the block given below it. If condition
evaluates result as false, it transfer the control at else part to test another condition. So, it
is multi-decision making construct.

Syntax:
if ( condition-1):
…………………..
…………………..
elif (condition-2):
…………………..
…………………..
elif (condition-3):
…………………..
…………………..
else:
…………………..
Example:
num=int(input(“Enter Number: “))
If ( num>=0):
Print(“You entered positive number”)
elif ( num<0):
Print(“You entered Negative number”)
else:
Print(“You entered Zero ”)
Python Nested if statements
It is the construct where one if condition take part inside of other if condition. This
construct consist of more than one if condition. Block executes when condition becomes
false and next condition evaluates when first condition became true.
So, it is also multi-decision making construct.
Syntax:

if ( condition-1):
if (condition-2):
……………
……………
else:
……………
……………
else:
…………………..
…………………..
Example:
num=int(input(“Enter Number: “))
If ( num<=0):
if ( num<0):
Print(“You entered Negative number”)
else:
Print(“You entered Zero ”)
else:
Print(“You entered Positive number”)

Program: find largest number out of given three numbers

x=int(input("Enter First Number: "))
y=int(input("Enter Second Number: "))
z=int(input("Enter Third Number: "))
if(x>y and x>z):
largest=x
elif(y>x and y>z):
largest=y
elif(z>x and z>y):
largest=z
print("Larest Value in %d, %d and %d is: %d"%(x,y,z,largest))
Python Iteration Statements
The iteration (Looping) constructs mean to execute the block of statements again
and again depending upon the result of condition. This repetition of statements
continues till condition meets True result. As soon as condition meets false result, the
iteration stops.
Python supports following types of iteration statements
1. while
2. for
Four Essential parts of Looping:
i. Initialization of control variable
ii. Condition testing with control variable
iii. Body of loop Construct
iv. Increment / decrement in control variable

Python while loop

The while loop is conditional construct that executes a block of statements again
and again till given condition remains true. Whenever condition meets result false then
loop will terminate.
Syntax:

Initialization of control variable while (condition):

…………………..
Updation in control variable
..…………………
Flowchart
Example: print 1 to 10 numbers

num=1 # initialization
while(num<=10): # condition testing
print(num, end=” “)

num + = 1 # Increment Body of loop

Example: Sum of 1 to 10 numbers.

num=1 sum=0
while(num<=10):
sum + = num
num + = 1
print(“The Sum of 1- 10 numbers: “,sum)
 Python range( ) Function
The range() function returns a sequence of numbers, starting from 0 by default, and
increments by 1 (by default), and ends at a specified number. The common format of range() is
as given below:
range ( start value, stop value, step value )

Where all 3 parameters are of integer type

Start and Step Parameters are
Start value is Lower Limit
Stop value is Upper Limit
optional default value will be as
Step value is Increment / Decrement Start=0 and Step=1
Note: The Lower Limit is included but Upper Limit is not included in result.
Example
range(5) => sequence of 0,1,2,3,4
range(2,5) => sequence of 2,3,4
range(1,10,2) => sequence of 1,3,5,7,9 r
ange(5,0,-1) => sequence of 5,4,3,2,1
range(0,-5) => sequence of [ ] blank list (default Step is +1)
range(0,-5,-1) => sequence of 0, -1, -2, -3, -4
range(-5,0,1) => sequence of -5, -4, -3, -2, -1
range(-5,1,1) => sequence of -5, -4, -3, -2, -1, 0

L=list(range(1,20,2)
Print(L) Output: [1, 3, 5, 7, 9, 11, 13, 15, 17, 19]

Python for loop

A for loop is used for iterating over a sequence (that is either a list, a tuple, a string
etc.) With for loop we can execute a set of statements, and for loop can also execute
once for each element in a list, tuple, set etc.

Example: print 1-10 numbers Example: print 10-1 numbers

for num in range(1,11,1): for num in range(10,0,-1):

print(num, end=” “) print(num, end=” “)

Output: 1 2 3 4 5 6 7 8 9 10 Output: 10 9 8 7 6 5 4 3 2 1

Print each element in a fruit list:

fruits = ["mango", "apple", "grapes", "cherry"]
for x in fruits:
print(x)

output: mango apple grapes cherry

else in for Loop

The else keyword in for loop specifies a block of code to be executed when the
loop is finished:

for x in range(4):
print(x, end=” “)
 else:
print("\nFinally finished!")
output: 0 1 2 3
Finally finished!
Nested Loops
A nested loop is a loop inside another loop.
city = ["Jaipur", "Delhi", "Mumbai"]
fruits = ["apple", "mango", "cherry"]
for x in city:
for y in fruits:
print(x, “:”,y)
output:
Jaipur : apple
Jaipur : mango
Jaipur : cherry
Delhi : apple
Delhi : mango
Delhi : cherry
Mumbai : apple
Mumbai : mango
Mumbai : cherry

Un- Conditional Control Construct

(pass, break, continue, exit(), quit())

pass Statement (Empty Statement)

The pass statement do nothing, but it used to complete the syntax of
programming concept. Pass is useful in the situation where user does not requires any
action but syntax requires a statement. The Python compiler encounters pass statement
then it do nothing but transfer the control in flow of execution.

a=int(input("Enter first Number: "))

b=int(input("Enter Second Number: "))
if(b==0):
pass
else:
print("a/b=",a/b)
 for x in [0, 1, 2]:
pass

Jumping Statements

break Statement
The jump- break statement enables to skip over a part of code that used in loop
even if the loop condition remains true. It terminates to that loop in which it lies. The
execution continues from the statement which find out of loop terminated by break.
n=1
while(n<=5):
print("n=",n)
k=1
while(k<=5):
if(k==3):
break
print("k=",k, end=" ")
k+=1
n+=1
print()
Output:
n= 1
k= 1 k= 2
n= 2
k= 1 k= 2
n= 3
k= 1 k= 2
n= 4
k= 1 k= 2
n= 5
k= 1 k= 2
Exit the loop when xis "banana":
fruits = ["apple", "banana", "cherry"]
for x in fruits:
if x == "banana":
b
reak
print(
x)

output: apple
Continue Statement
Continue statement is also a jump statement. With the help of continue
statement, some of statements in loop, skipped over and starts the next iteration. It
forcefully stop the current iteration and transfer the flow of control at the loop
controlling condition.

i=0
while i <=10:
i+=1
if (i%2==1):
continue
print(I, end=” “)
output: 2 4 6 8
10

fruits = ["apple", "banana", "cherry"]

for x in fruits:
if x == "banana":
continue
print(x)
output:
apple
cherry