Control Statement in Python IF, Else and Elif
Control Statement in Python
Python statements are executed one by one in the same order
as the appear in the program. But there may be some requirement when we want to
execute the statements based upon a condition. Even there may be some situation
where we want to execute a single statement or multiple statement (Block of
statement) “n” times till the condition is true. So in orde to control the flow
of execution of the program Python provides us Control Statements.
पायथन स्टेटमेंट को एक-एक करके उसी क्रम में निष्पादित किया जाता है
जैसे प्रोग्राम में दिखाई देता है। लेकिन कुछ आवश्यकता हो सकती है जब हम किसी शर्त
के आधार पर कथनों को निष्पादित करना चाहते हैं। यहां तक कि कुछ ऐसी स्थिति भी हो
सकती है जहां हम एक ही कथन या एकाधिक कथन (स्टेटमेंट का ब्लॉक) "एन" बार
निष्पादित करना चाहते हैं जब तक कि शर्त सत्य न हो। तो कार्यक्रम के निष्पादन के
प्रवाह को नियंत्रित करने के लिए पायथन हमें नियंत्रण विवरण प्रदान करता है।
There are two types of control statements:
Ø
Selection statement: - IF, Else, IF Elif
Else
Ø
Looping Conditions: - For, While
1.
Selection statement: - Selection statements are
used to select the statements based on a condition. In other words, we can say
that if there is some condition based upon which it is decided that whether a
statement will be executed or not, then this is called selection statement.
Python provides us “if” selection statement. एक शर्त के आधार पर बयानों का चयन करने
के लिए चयन विवरण का उपयोग किया जाता है। दूसरे शब्दों में हम कह सकते हैं कि यदि
कोई ऐसी शर्त है जिसके आधार पर यह निर्णय लिया जाता है कि किसी कथन को क्रियान्वित
किया जाएगा या नहीं, तो इसे चयन कथन कहते हैं। पायथन हमें "IF" चयन विवरण प्रदान करता है।
IF, IF Else, If Elif Else
If is a bi-directional conditional
control statement that checks the condition and work according to that
condition. A condition may have only two result – either the condition is true
or the condition is false.
Syntax 1:
If condition
Statement
1
Statement
2
---------------
Statement
n
Syntax 2:
If condition
Statement
1
-----------------
Else
Statement
1
----------------
Syntax 3:
If condition
Statement
1
-----------------
Elif condition
Statement
1
----------------
Else
Statement
1
----------------
Python supports the usual
logical conditions from mathematics:
- Equals: a == b
- Not
Equals: a! = b
- Less
than: a < b
- Less
than or equal to: a <=
b
- Greater
than: a > b
- Greater
than or equal to: a >= b
These conditions can be
used in several ways, most commonly in "if statements" and loops.
An "if statement"
is written by using the if keyword.
Example
If
statement:
a
= 33
b = 200
if b > a:
print("b
is greater than a")
Output: b
is greater than a
In this example we use two
variables, a and b, which are used as part of the if statement to
test whether b is greater
than a. As a is 33, and b is 200, we know that 200 is greater than 33, and so we
print to screen that "b is greater than a". इस उदाहरण
में हम दो Variables, a और b का उपयोग करते हैं, जिनका उपयोग if कथन के भाग के रूप
में यह परीक्षण करने के लिए किया जाता है कि क्या b, a से बड़ा है। जैसा कि a 33 है, और b 200 है, हम जानते हैं कि 200, 33 से बड़ा है, और इसलिए हम स्क्रीन
पर प्रिंट करते हैं कि "b, a से बड़ा है"।
Indentation
Python relies on indentation (whitespace at the beginning of a
line) to define scope in the code. Other programming languages often use
curly-brackets for this purpose. कोड में स्कोप को परिभाषित करने के लिए Python इंडेंटेशन (एक लाइन की शुरुआत में व्हाइटस्पेस) पर निर्भर
करता है। अन्य प्रोग्रामिंग भाषाएं अक्सर इस उद्देश्य के लिए curly-कोष्ठक का उपयोग करती हैं।
Example
If
statement, without indentation (will raise an error):
a
= 33
b = 200
if b > a:
print ("b
is greater than a") # you will get an error
Elif
The elif keyword is pythons way of
saying "if the previous conditions were not true, then try this
condition".
Example
a
= 33
b = 33
if b > a:
print("b
is greater than a")
elif a == b:
print("a
and b are equal")
In this example a is
equal to b, so the first condition is not true,
but the elif condition is true, so we
print to screen that "a and b are equal".
Output: a
and b are equal
Else
The else keyword catches anything
which isn't caught by the preceding conditions.
Example
a
= 200
b = 33
if b > a:
print("b
is greater than a")
elif a == b:
print("a
and b are equal")
else:
print("a
is greater than b")
Output: a
is greater than b
In this example a is
greater than b, so the first condition is not true, also the elif condition
is not true, so we go to the else condition
and print to screen that "a is greater than b".
You can also have an else without
the elif:
Example
a
= 200
b = 33
if b > a:
print("b
is greater than a")
else:
print("b
is not greater than a")
Output: b
is not greater than a
Short Hand If
If you have only one statement to execute, you can put it on
the same line as the if statement.
Example
One
line if statement:
if a > b: print("a
is greater than b")
Output: a
is greater than b
Short Hand If
... Else
If you have only one statement to execute, one for if, and
one for else, you can put it all on the same line:
Example
One
line if else statement:
a
= 2
b = 330
print("A") if a > b else print("B")
Output: B
This technique is known as Ternary Operators,
or Conditional Expressions.
You can also have multiple else statements on the same line:
Example
One
line if else statement, with 3 conditions:
a
= 330
b = 330
print("A") if a > b else print ("=") if a == b else print("B")
Output: =
And
The and keyword is a logical
operator, and is used to combine conditional statements:
Example
Test
if a is greater than b, AND
if c is greater than a:
a
= 200
b = 33
c = 500
if a > b and c > a:
print("Both
conditions are True")
Output: Both
conditions are true
Or
The or keyword is a logical
operator, and is used to combine conditional statements:
Example
Test
if a is greater than b, OR
if a is greater than c:
a
= 200
b = 33
c = 500
if a > b or a > c:
print("At
least one of the conditions is True")
Output: At
least one of the conditions is true
Nested If
You can have if statements
inside if statements, this is called nested if statements.
Example
x
= 41
if x > 10:
print("Above
ten,")
if x
> 20:
print("and
also above 20!")
else:
print("but
not above 20.")
Output: Above
ten,
And also above 20!
The pass
Statement
if statements cannot be empty, but if you for some reason have
an if statement with no content, put in the pass statement
to avoid getting an error.
Example
a
= 33
b = 200
if b > a:
pass
Output:
Example
A = int (input (“Enter
number to check:”);
If a%2==0:
Print (“Number is even”)
Output: Enter Number to
check: 20
Number is even
Example
A = int (input (“Enter
number to check:”);
If a%2==0:
Print (“Number is even”)
Else:
Print (“Number is Odd”)
Output: Enter Number to
check: 15
Number is odd
Example
A = int (input (“Enter
number to check:”);
If a>60:
Print (“First Division”)
Elif a>50:
Print (“Second Division”)
Elif a>40:
Print (“Third Division”)
Else:
Print (“Fail”)
Output: Enter
number to check:55
Second Division
Exercise:
Print
"Hello World" if a is greater than b.
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