3: Conditional Statements
3.2 IF, IF-ELSE, AND IF-ELIF-ELSE CONSTRUCTS
3.1 INTRODUCTION
The preceding chapters presented the basic data types and simple
statements in Python. The concepts studied so far are good for the execution of
a program which has no branches. However, a programmer would seldom find a
problem solving approach devoid of branches.
Before proceeding any further let us spare some time
contemplating life. Can you move forward in life without making decisions? The
answer is NO. In the same way the problem solving approach would not yield
results until the power of decision making is incorporated. This is the reason
one must understand the implementation of decision making and looping. This
chapter describes the first concept. This is needed to craft a program which
has branches. Decision making empowers us to change the control-flow of the
program. In C, C++, Java, C#, etc., there are two major ways to accomplish the
above task. One is the ‘if’
construct and the other is ‘switch’. The
‘if’ block in a program
is executed if the ‘test’
condition is true otherwise it is not executed. Switch is used to implement a scenario in which there are many ‘test
’ conditions, and the corresponding block executes in case a
particular test condition is true.
The chapter introduces the concept of conditional statements,
compound statements, the if-elif ladder
and finally the get
statement.
The chapter assumes importance as conditional statements are used in every
aspect of programming, be it client side development, web development, or
mobile application development.
The chapter has been organized as follows. The second section
introduces the ‘if’
construct. Section 3.3 introduces ‘if-elif’ ladder. Section 3.4 discusses
the use of logic operators. Section 3.5 introduces
ternary operators. Section 3.6 presents the get
statement and the last section concludes the chapter. The
reader is advised to go through the basic data types before proceeding further.
3.2 IF, IF-ELSE,
AND IF-ELIF-ELSE
CONSTRUCTS
Implementing decision making gives the power to incorporate
branching in a program. As stated earlier, a program is a set of instructions
given to a computer. The instructions are given to accomplish a task and any
task requires making decisions. So, conditional statements form an integral
part of programming. The syntax of the construct is as follows:
General Format
1.
if
3.
if <test condition>:
4.
<block if the test condition is true>
5.
if-else
7.
if <test condition>:
8.
<block if the test condition is true>
9.
else:
10.
<block if the test
condition is not true>
11.
...
12. If else ladder (discussed
in the next section)
14.
if <test condition>:
15.
<block if the test
condition is true>
16.
elif <test 2>:
17.
<second block>
18.
elif <test 3>:
19.
<third block>
20.
else:
21.
<block if the test
condition is true>
Note
that indentation is important, as Python recognizes a block through
indentation. So, make sure that the 'if (<condition>):'
is followed by a
block, each statement of which is at the same alignment. In order to understand
the concept, let us consider a simple example. A student generally clears a
university exam in India if he scores more than 40%. In order to implement the
logic, the user is asked to enter the value of the percentage. If the
percentage entered is more than 40 then “exam cleared” is
printed, otherwise “failed” is printed. The
situation has been depicted in the following figure (Figure 3.1).
Figure 3.1: Flow chart for example 1
Illustration
3.1
Ask the user to enter the marks of a student in a subject. If
the marks entered are greater than 40 then print “pass,” if
they are lower print “fail.”
Program
>>>a
= input("Enter marks : ")
if
int(a)> 40:
print('Pass')
else:
print('Fail')
...
Output 1
Enter
Marks : 50
Pass
Output 2
Enter
Marks : 30
Fail
Let us have a look at another example. In the problem, the user
is asked to enter a three digit number to find the number obtained by reversing
the order of the digits of the number; then find the sum of the number and that
obtained by reversing the order of the digits and finally, find whether this
sum contains any digit in the original number. In order to accomplish the task,
the following steps (presented in Illustration 3.2) must be carried out.
Illustration
3.2
Ask the user to enter a three digit number. Call it 'num'
. Find the number obtained
by reversing the order of the digits. Find the sum of the given number and that
obtained by reversing the order of the digits. Finally, find if any digit in
the sum obtained is the same as that in the original number.
Solution:
The problem can be solved as follows:
·
When the user enters a number, check whether it is between 100
and 999, both inclusive.
·
Find the digits at unit’s, ten’s and hundred’s place. Call
them 'u', 't' and 'h'
respectively.
·
Find the number obtained by reversing the order of the digits
(say, ‘rev’) using the following formula.
·
Number obtained by reversing the order of the digits, rev = h + t × 10 + u × 100
·
Find the sum of the two numbers.
Sum = rev + num
·
The sum may be a three digit or a four digit number. In any
case, find the digits of this sum. Call them 'u1', 't1', 'h1' and 'th1'
(if required).
·
Set 'flag=0'
.
·
Check the following condition. If any one is true, set the value
of flag to 1. If “sum” is a three digit
number
u = = u1
u = = t1
u = = h1
t = = u1
t = = t1
t = = h1
h = = u1
h = = t1
h = = h1
·
If “sum” is a four digit
number the above conditions need to be checked along with the following
conditions:
u = = th1
h = = th1
t = = th1
·
The above conditions would henceforth be referred to as “set 1.” If the value of “flag” is
1, then print 'true' else print 'false'
.
·
The above process has been depicted in the following figure (Figure
3.2).
Program
num=int(input('Enter
a three digit number\t:'))
if
((num<100) | (num>999)):
print('You have not entered a number
between 100 and 999')
else:
flag=0
o=num%10
t=int(num/10)%10
h=int(num/100)%10
print('o\t:',str(o),'t\t:',str(t),'h\t:',str(h))
rev=h+t*10+o*100
print('Number obtained by reversing the
order of the
digits\t:',str(rev))
sum1=num+rev
print('Sum of the number and that obtained
by
reversing the order of
digits\t:',str(sum1))
if sum1<1000:
o1=sum1%10
t1=int(sum1/10)%10
h1=int(sum1/100)%10
print('o1\t:',str(o1),'t1\t:',str(t1),'h1\t:',str(h1))
if
((o==o1)|(o==t1)|(o==h1)|(t==o1)|(t==t1)|
(t==h1)|(h==o1)|(h==t1)|(h==h1)):
print('Condition true')
flag==1
else:
o1=sum1%10
t1=int(sum1/10)%10
h1=int(sum1/100)%10
th1=int(sum1/1000)%10
print('o1\t:',str(o1),'t1\t:',str(t1),'h1\
t:',str(h1),'t1\t:',str(t1))
if ((o==o1)|(o==t1)|(o==h1)|(o==th1)|(t==o1)|(t==t1)|
(t==h1)|(t==th1)|(h==o1)|(h==t1)|(h==h1)|(h==th1)):
print('Condition true')
flag==1
Output: First run
>>>
=========
RUN C:/Python/Conditional/Problem 2.py =========
Enter
a three digit number :4
You
have not entered a number between 100 and 999
>>>
Output: Second run
>>>
=========
RUN C:/Python/Conditional/Problem 2.py =========
Enter
a three digit number :343
o
: 3 t : 4 h : 3
Number
obtained by reversing the order of the digits : 343
No
digit of the sum is same as the original number
>>>
Output: Third run
>>>
=========
RUN C:/Python/Conditional/Problem 2.py =========
Enter
a three digit number : 435
o
: 5 t : 3 h : 4
Number
obtained by reversing the order of the digits : 534
No
digit of the sum is same as the original number
>>>
Output: Fourth run
>>>
=========
RUN C:/Python/Conditional/Problem 2.py =========
Enter
a three digit number :121
o
: 1 t : 2 h : 1
Number
obtained by reversing the order of the digits : 121
Sum
of the number and that obtained by reversing the order of digits : 242
o1
: 2 t1 : 4 h1 : 2
Condition
true
>>>
.
Tip
One must be careful regarding the indentation, failing which the
program would not compile. The indentation decides the beginning and ending of
a particular block in Python. It is advisable not to use a combination of
spaces and tabs in indentation. Many versions of Python may treat this as a
syntax error.
The if-elif
ladder can also be
implemented using the get statement, explained later in the chapter. The
important points regarding the conditional statements in Python are as follows:
·
The if <test> is followed by a colon.
·
There is no need of parentheses for this test condition. Though
enclosing test in parentheses will not result in an error.
·
The nested blocks in Python are determined by indentation.
Therefore, proper indentation in Python is essential. As a matter of fact, an
inconsistent indentation or no indentation will result in errors.
·
An if can have any number
of if's
nested within.
·
The test condition in if must result in a True or a False
.
Illustration
3.3
Write a program to find the greatest of the three numbers
entered by the user.
Solution: First of all, three variables (say num1, num2, and num3
) are needed. These
variables will get their values from the user. This input will be followed by
the condition checking as depicted in the following program. Finally, the
greatest number will be displayed. The listing is given as follows:
Program
>>>num1
= input('Enter the first number\t:')
...num2
= input('Enter the second number\t:')
...num3
= input('Enter the third number\t:')
...if
int(num1)> int(num2):
...
if int(num1) > int(num3):
...
big= int(num1)
...
else:
...
big = int(num2)
...
...else:
...
if int(num2)> int(num3)
...
big= num2
...
else:
...
big = num3
...
...
...print(big)
3.3 THE IF-ELIF-ELSE
LADDER
If there are multiple conditions and the outcomes decide the
action, then an if-
elif- else
ladder
can be used. This section discusses the construct and presents the concept
using relevant examples. The syntax of this construct is as follows:
Syntax
if
<test condition 1>:
# The task to be performed if the condition
1 is true
elif
<test condition 2>:
# The task to be performed if the condition
2 is true
elif
<test condition 3>:
# The task to be performed if the condition
1 is true
else:
# The task to be performed if none of the
above condition is true
The
flow of the program can be managed using the above construct. Figure
3.3 shows the diagram depicting the flow of the program which
uses the above constructs.
Figure 3.3: The flow graph of if and elif ladder
In
the figure, the left edge depicts the scenario where the condition C is true
and the right edge depicts the scenario where the condition is false. In the
second graph, conditions C1, C2, C3, and C4 lead to different paths [Programming in C#, Harsh
Bhasin, 2014].
The
following section has programs that depict the use of the elif ladder. It may be
noted that if there are multiple else statements, then the second else is taken along with
the nearest if
.
3.4 LOGICAL OPERATORS
In many cases the execution of a block depends on the truth
value of more than one statement. In such cases the operators “and” (“&”) and “or” (“|”) come to our rescue.
The first ('and') is used when the output
is 'true', when both the
conditions are 'true'. The second ('or') is used if the output
is 'true', if any of the conditions
are 'true'
.
The
truth table of 'and' and 'or'
is given as follows.
In the tables that follow “T” stands
for “true” and “F” stands
for “false.”
|
a
|
b
|
a&b
|
|
<p>t</p>
|
T
|
T
|
|
<p>t</p>
|
F
|
F
|
|
<p>F</p>
|
T
|
F
|
|
<p>F</p>
|
F
|
F
|
print('The value of a greatest')
|
Table 3.2: Truth table
of a|b
|
||
|
a
|
b
|
a|b
|
|
<p>t</p>
|
T
|
T
|
|
<p>t</p>
|
F
|
T
|
|
<p>F</p>
|
T
|
T
|
|
<p>F</p>
|
F
|
F
|
The
above statement helps the programmer to easily handle compound statements. As
an example, consider a program to find the greatest of the three numbers
entered by the user. The numbers entered by the user are (say) 'a', 'b', and 'c', then 'a' is greatest if (a > b) and (a > c)
. This can be written as follows:
if((a>b)&(a>c))
In
the same way, the condition of ‘b’
being greatest can be crafted. Another example can be that of a triangle. If
all the three sides of a triangle are equal, then it is an equilateral
triangle.
if((a==b)
or (b==c) or (c==a))
//The triangle is isosceles;
3.5 THE TERNARY OPERATOR
The conditional statements explained in the above section are
immensely important to write any program that contains conditions. However, the
code can still be reduced further by using the ternary statements provided
by Python. The ternary operator performs the same task as the if-else
construct. However, it has the same disadvantage as in the case of C or C++.
The problem is that each part caters to a single statement. The syntax of the
statement is given as follows.
Syntax
<Output
variable> = <The result when the condition is
true>
if
<condition> else <The result when the condition is not
true>
For example, the conditional operator can be used to check which of the two numbers entered by the user is greater.
great
= a if (a>b) else b
Finding the greatest of the three given numbers is a bit intricate. The following statement puts the greatest of the three numbers in “great.”
great
= a if (a if (a > b) else c)) else(b if (b>c) else c))
The
program that finds the greatest of the three numbers entered by the user using
a ternary operator is as follows.
Illustration
3.4
Find the greatest of three numbers entered by the user, using a
ternary operator.
Program
a
= int(input('Enter the first number\t:'))
b
= int(input('Enter the second number\t:'))
c
= int(input('Enter the third number\t:'))
big
= (a if (a>c) else c) if (a>b) else (b if (b>c) else c)
print('The
greatest of the three numbers is '+str(big))
>>>
Output
==========
RUN C:/Python/Conditional/big3.py ==========
Enter
the first number 2
Enter
the second number 3
Enter
the third number 4
The
greatest of the three numbers is 4
>>>
3.6 THE GET CONSTRUCT
In C or C++ (even in C# and Java) a switch is used in the case
where different conditions lead to different actions. This can also be done
using the 'if-elif' ladder, as explained
in the previous sections. However, the get
construct greatly eases this task in the
case of dictionaries.
In
the example that follows there are three conditions. However, in many
situations there are many more conditions. The contact can be used in such
cases. The syntax of the construct is as follows:
Syntax
<dictionary
name>.get('<value to be searched>',
'default value>')
Here,
the expression results in some value. If the value is value 1, then block 1 is executed.
If it is value 2, block 2 is executed, and
so on. If the value of the expression does not match any of the cases, then the
statements in the default
block are executed.
Illustration 5 demonstrates the use of the get construct.
Illustration
3.5
This illustration has a directory containing the names of books
and the corresponding year they were published. The statements that follow find
the year of publication for a given name. If the name is not found the string
(given as the second argument, in get) is displayed.
Program
hbbooks
= {'programming in C#': 2014, 'Algorithms': 2015, 'Python': 2016}
print(hbbooks.get('Programming
in C#', 'Bad Choice'))
print(hbbooks.get('Algorithms',
'Bad Choice'))
print(hbbooks.get('Python',
'Bad Choice'))
print(hbbooks.get('Theory
Theory, all the way', 'Bad Choice'))
Output
>>>
==========
RUN C:/Python/Conditional/switch.py ==========
Bad
Choice
2015
2016
Bad
Choice
>>>
Note that in the first case the “P” of “Programming” is capital, hence “Bad
Choice” is displayed. In the second and the third cases, the get
function is able to find the requisite value. In the last case the value is not
found and so the second argument of the get function appears. Note that it is
similar to the default of the “C” type switch
statement. The flow
diagram given in Figure 3.4 shows a program that has many
branches.
Observation
In Python, dictionaries and lists form an integral part of the
language basics. The use of the get
construct was not explained in Chapter 2 of this book, as it implements
the concept of conditional selection. It may be noted that this construct
greatly reduces the problems of dealing with the situations where mapping is
required and is therefore important.
3.7 EXAMPLES
The 'if'
condition is also
used for input validation. The process will be explained in the following
sections of this book. However, the idea has been used in the example that
follows. The program asks the user to enter a character and checks whether its
ASCII value is greater a certain value.
Illustration
3.6
Ask the user to enter a number and check whether its ASCII value
is greater than 80.
Program
inp
= input('Enter a character :')
if
ord(inp) > 80:
print('ASCII value is greater than 80')
else:
print('ASCII value is less than 80')
Output
1:
>>>Enter
a character: A
ASCII
value is less than 80
...
Output 2
>>>Enter
a character: Z
ASCII
value is greater than 80
>>>
The construct can also be used to find the value of a
multi-valued function. For example, consider the following function:
The following example asks the user to enter the value of x and calculates the value of the function as per the given value of x.
Illustration
3.7
Implement the above function and find the values of the function
at x = 2 and x = 4
.
Program
fx
= """
f(x)
= x^2 + 5x + 3 , if x > 2
=
x + 3 , if x <= 2
"""
x
= int (input('Enter the value of x\t:'))
if
x > 2:
f
= ((pow(x,2)) + (5*x) + 3)
else:
f
= x + 3
print('Value
of function f(x) = %d' % f )
Output
==========
RUN C:\Python\Conditional\func.py ==========
Enter
the value of x :4
Value
of function f(x) = 39
>>>
==========
RUN C:\Python\Conditional\func.py ==========
Enter
the value of x :1
Value
of function f(x) = 4
>>>
The 'if-else'
construct, as stated
earlier, can be used to find the outcome based on certain conditions. For
example, two lines are parallel if the ratio of the coefficients of x’s is the same
as that of those of y’s.
For a1x + b1y + c1 = 0
and a2x + b2y + c2 = 0. Then
the condition of lines being parallel is:
The following program checks whether two lines are
parallel or not.
Illustration
3.8
Ask the user to enter the coefficients of a1x + b1y + c1 = 0
and a2x + b2y + c2 = 0 and
find out whether the two lines depicted by the above equations are parallel or
not.
Program
print('Enter
Coefficients of the first equation [a1x + b1y + c1
= 0]\n')
r1
= input('Enter the value of a1: ')
a1
= int (r1)
r1
= input('Enter the value of b1: ')
b1
= int (r1)
r1
= input('Enter the value of c1: ')
c1
= int (r1)
print('Enter
Coefficients of second equation [a2x + b2y + c2 = 0]\n')
r1
= input('Enter the value of a2: ')
a2
= int (r1)
r1
= input('Enter the value of b2: ')
b2
= int (r1)
r1
= input('Enter the value of c2: ')
c2
= int (r1)
if
(a1/a2) == (b1/b2):
print('Lines are parallel')
else:
print('Lines are not parallel')
Output
>>>
==========
RUN C:\Python\Conditional\parallel.py ==========
Enter
Coefficients of the first equation [a1x + b1y + c1
= 0]
Enter
the value of a1: 2
Enter
the value of b1: 3
Enter
the value of c1: 4
Enter
Coefficients of second equation [a2x + b2y + c2
= 0]
Enter
the value of a2: 4
Enter
the value of b2: 6
Enter
the value of c2: 7
Lines
are parallel
>>>
The above program can be extended to find whether the lines are
intersecting or overlapping: two lines intersect if the following condition is
true.
a1x
+ b1y + c1 = 0
and a2x + b2y + c2 = 0. Then
the lines intersect if:
And the two lines overlap if:
The following flow-chart shows the flow of control of
the program (Figure 3.5).
The following program implements the above logic.
Illustration
3.9
Ask the user to enter the values of a1, a2, b1, b2, c1, and c2 and find
whether the lines are parallel, or if they overlap or intersect.
Program
print('Enter
Coefficients of the first equation [a1x + b1y
+ c1 = 0]\n')
r1
= input('Enter the value of a1: ')
a1
= int (r1)
r1
= input('Enter the value of b1: ')
b1
= int (r1)
r1
= input('Enter the value of c1: ')
c1
= int (r1)
print('Enter
Coefficients of second equation [a2x + b2y + c2
= 0 ]\n')
r1
= input('Enter the value of a2: ')
a2
= int (r1)
r1
= input('Enter the value of b2: ')
b2
= int (r1)
r1
= input('Enter the value of c2: ')
c2
= int (r1)
if
((a1/a2) == (b1/b2))&((a1/a2)==(c1/c2)):
print('Lines overlap')
elif
(a1/a2)==(b1/b2):
print('Lines are parallel')
else:
print('Lines intersect')
Output
>>>
==========
RUN C:/Python/Conditional/Lines.py ==========
Enter
Coefficients of the first equation [a1x + b1y + c1
= 0]
Enter
the value of a1: 2
Enter
the value of b1: 3
Enter
the value of c1: 4
Enter
Coefficients of second equation [a2x + b2y + c2
= 0]
Enter
the value of a2: 1
Enter
the value of b2: 2
Enter
the value of c2: 3
Lines
intersect
3.8 POINTS TO REMEMBER
- The 'if' statement implements conditional branching.
- The test
condition is a Boolean expression which results in a true or a false.
- The block
of 'if' executes
if the test condition it true.
- The else part executes if the test condition is false.
- Multiple
branches can be implemented using the if-elif ladder.
- Any number
of if-elif can be
nested.
- A ternary if can be implemented in Python.
- Logical
operators can be used in implementing conditional statements.
3.9 EXERCISES
MULTIPLE CHOICE QUESTIONS
1.
What will be the output of the following?
if 28:
print('Hi')
else:
print('Bye')
a.
Hi
b.
Bye
c.
None of the above
d.
The above snippet will not compile
Answer:
(a)
2.
a
= 5
b = 7
c = 9
if a>b:
if b>c:
print(b)
else:
print(c)
else:
if b>c:
print(c)
else:
print(b)
a.
7
b.
9
c.
34
d.
None of the following
Answer:
(a)
3.
a
= 34
b = 7
c = 9
if a>b:
if b>c:
print(b)
else:
print(c)
else:
if b>c:
print(c)
else:
print(b)
a.
7
b.
9
c.
None of the above
d.
The code will not compile
Answer:
(b)
4.
a
= int(input('First number\t:'))
b = int(input('Second
number\t'))
c = int(input('Third
number\t:'))
if ((a>b) &
(a>c)):
print(a)
elif ((b>a)
&(b>c)):
print(b)
else:
print(c)
a.
The greatest of the three numbers entered by the user
b.
The smallest of the three numbers entered by the user
c.
None
d.
The code will not compile
Answer:
(a)
5.
n
= int(input('Enter a three digit number\t:'))
if (n%10)==(n//100):
print('Hi')
else:
print('Bye')
# The three digit
number entered by the user is 453
a.
Hi
b.
Bye
c.
None of the above
d.
The code will not compile
Answer:
(b)
6.
In the above question, if the number entered is 545, what would
the answer be?
a.
Hi
b.
Bye
c.
None of the above
d.
The code will not compile
Answer:
(a)
7.
hb1 = ['Programming
in C#','Oxford University Press', 2014]
hb2 = ['Algorithms', 'Oxford University
Press', 2015]
if hb1[1]==hb2[1]:
print('Same')
else:
print('Different')
a.
same
b.
Different
c.
No output
d.
The code would not compile
Answer:
(a)
8.
hb1
= ['Programming in C#','Oxford University Press', 2014]
hb2 = ['Algorithms',
'Oxford University Press', 2015]
if (hb1[0][3]==hb2[0][3]):
print('Same')
else:
print('Different')
a.
Same
b.
Different
c.
No output
d.
The code will not compile
Answer:
(b)
9.
In the snippet given in question 8, the following changes are
made. What will the output be?
hb1 = ['Programming in C#','Oxford
University Press', 2014]
hb2 = ['Algorithms', 'Oxford University
Press', 2015]
if (str(hb1[0][3])==str(hb2[0][3])):
print('Same')
else:
print('Different')
a.
Same
b.
Different
c.
No output
d.
The code will not compile
Answer:
(b)
10.
Finally, the code in question 8 is changed to the following.
What will the output be?
hb1 = ['Programming in C#','Oxford
University Press', 2014]
hb2 = ['Algorithms', 'Oxford University
Press', 2015]
if (char(hb1[0][3])==char(hb2[0][3])):
print('Same')
else:
print('Different')
a.
Same
b.
Different
c.
No output
d.
The code will not compile
Answer:
(b)
3.10 PROGRAMMING EXERCISE
1.
Ask the user to enter a number and find the number obtained by
reversing the order of the digits.
2.
Ask the user to enter a four digit number and check whether the
sum of the first and the last digits is same as the sum of the second and the
third digits.
3.
In the above question if the answer is true then obtain a number
in which the second and the third digit are one more than that in the given
number.
Example: Number 5342, sum of the first and the last digit = 7 that of the
second and the third digit = 7. New number: 5452
4.
Ask the user to enter the concentration of hydrogen ions
in a given
solution (C) and find the PH of the solution using the following formula.
PH = log10 C
5.
If the PH is <7 then the solution is deemed acidic, else it
is deemed as basic. Find if the given solution is acidic.
6.
In the above question find whether the solution is neutral. (A
solution is neutral if the PH is 7)
7.
The centripetal force acting on a body (mass m), moving with a
velocity v, in
a circle of radius r,
is given by the formula mv2/r. The gravitational force on
the body is given by the formula (GmM)/R2, where m and M are the masses
of the body and earth and R is the radius of the earth. Ask the user to enter
the requisite data and find whether the two forces are equal or not.
8.
Ask the user to enter his salary and calculate the TADA, which
is 10% of the salary; the HRA, which is 20% of the salary and the gross income,
which is the sum total of the salary, TADA and the HRA.
9.
In the above question find whether the net salary is greater
than $300,000.
10. Use the Tax Tables of the
current year to find the tax on the above income (question number 8), assuming
that the savings are $100,000.
11. Find whether a number
entered by the user is divisible by 3 and 13.
12. Find whether the number
entered by the user is a perfect square.
13. Ask the user to enter a
string and find the alphanumeric characters from the string.
14. In the above question find
the digits in the strings.
15. In question 13, find all
the components of the string which are not digits or alphabets.
