Python Programming Notes (BVOC 4th SEM) UNIT-2

Conditional Statements

There are situations in real life when we need to do some specific task and based on some specific conditions, we decide what we should do next. Similarly, there comes a situation in programming where a specific task is to be performed if a specific condition is True. In such cases, conditional statements can be used. The following are the conditional statements provided by python-

if
if-else
Nested-if
if-elif

1) if Statement

The ‘if’ statement is written using “if” keyword, followed by a condition.If the condition is true the statement-1 will be executed. Otherwise, the control will be transferred to the first statement after the if block that is statement-2 will be executed.

if statement must be followed by colon (:)
Indentation (white space) must be used after if statement as shown below example

Syntax:

if <condition>:
statement-1

statement-2

Example-

if 10>5:

print("10 is largest number")

print("Program end")

Note - If you have only one statement in if statement then you can write it in one line as below

if 10>5: print("10 is largest")

2) if else Statement

If the condition is true the statement-1 will be executed. Otherwise, the else block that is statement-2 will be executed.

if and else statement must be followed by colon (:)
Indentation (white space) must be used after if and else statement as shown below example

Syntax:

if <condition>:

statement-1

else:

statement-2

Example-

   if 10>5:
    print("10 is largest number")
   else:

print("5 is largest number")

3) Nested if Statement

If we use if statement inside another if statement or else statement then it is known as nested if statement.

if and else statement must be followed by colon (:)
Indentation (white space) must be used after if and else statement as shown below example

Syntax:

if <condition-1>:

statement-1

else:

if<condition-2>:

statement-2

else:

if<condition...N>:

statement...N

else

statement..M

Example-

ch='b'

if ch=='a':

print("Input character is a")

else:

if ch=='b':

print("Input character is b")

else:

if ch=='c':

print("Input character is c")

else:

print("Input character is not a or b or c")

4) if-elif Statement

if-elif statement is an updated form of nested if statement. The elif keyword means "else if "followed by any condition is used when previous if condtiton is not true

if and else statement must be followed by colon (:)
Indentation (white space) must be used after if and else statement as shown below example

Syntax:

if <condition-1>:

statement-1

elif<condition-2>:

statement-2

elif<condition...N>:

statement...N

else

statement..M

Example-

ch='a'

if ch=='d':

print("Input character is a")

elif ch=='b':

print("Input character is b")

elif ch=='c':

print("Input character is c")

else:

print("Input character is not a or b or c")

Iterative Statements or Loop Statements

Sometimes certain section of the code (block) may need to be repeated again and again as long as certain condition remains true. In order to achieve this, the iterative statements or loop statements are used.The number of times the block needs to be repeated is controlled by the test condition used in that statement. This type of statement is also called as the “Looping Statement”.

There are two types of loop in python-

for loop
while loop

1) for loop

The for loop is one of the powerful and efficient statements in python which is used very often. It specifies how many times the body of the loops needs to be executed. For this reason it uses control variables which keep tracks,the count of execution. The general syntax of a ‘for’ loop looks as below-

Syntax:

for <variable> in range (A,B):

body of the loop

Where A is the starting value and B is the end value + 1

Example

total = 0

n = int (input ("Enter a Positive Number"))

print("\n values are :",end=" ")

for i in range(1,n+1):

print(i,end=" ")

total = total + i

print ("\n The Sum is ", total)

range( ) Function

The range() function can be called in three different ways based on the number of parameters. All parameter values must be integers.

i) range(end) - This is begins at 0. Increments by 1. end just before the value of end parameter.

Example

for i in range(5):

print(i)

Output : 0,1,2,3,4

ii) range(beg, end) - Starts at begin, End before end value, Increment by 1

Example

for i in range(2, 5):

print(i)

Output : 2,3,4

iii) range(beg, end,step) - Starts at begin, End before end value, increment by step value

Example

for i in range(2, 7, 2):

print(i)

Output : 2,4,6

2) while loop

The while loop allows the program to repeat the body of a loop, any number of times, when some condition is true.The drawback of while loop is that, if the condition not proper it may lead to infinite looping. So the user has to carefully choose the condition in such a way that it will terminate at a particular stage.

Syntax:

while <condition>:

body of the loop

Example

total = 0

n = int (input ("Enter a Positive Number"))

i=1

while i<n:

total = total + i

i=i+1

print ("\n The Sum is ", total)

Nested loop

A nested loop is a loop inside a loop.The "inner loop" will be executed one time for each iteration of the "outer loop".

Example-

for i in range(1,6):
   for j in range(1,6):
       print(j,end='')
   print()

Break Statement

A break statement is used inside both the while and for loops. It terminates the loop immediately and transfers execution to the new statement after the loop.

For example

count = 0

while count <= 100:

print (count)

count += 1

if count == 3:

break

Output

Continue Statement

he continue statement causes the loop to skip its current execution at some point and move on to the next iteration. Instead of terminating the loop like a break statement, it moves on to the subsequent execution.

For example

for i in range(0, 5):

if i == 3:

continue

print(i)

Output