Decision Control Statements
if else Statement in Python
In this post, we are going to discuss Decision Control Statements in Python
but before these, if You are not seen our video on this topic please see it
first, then you will understand the concepts very well.
·
The if Statement
·
Concept of Indentation
·
The if-else Statement
·
The if - elif - else Statement
Decision Control Statements
in Python are those statements which decide the execution flow of
our program.
In other words, they allow us to decide whether a
particular part of our program should run or not based
on certain conditions.
The 4 decision control statements in Python are:
—
if
—
if….else
—
if…elif…else
—
nested if
The if Statement
The if the statement in Python is similar to other languages like
in Java, C, C++, etc.
It is used to decide whether a certain statement or block of statements
will be executed or not.
If a certain condition is true then a block of statement is executed
otherwise not.
—
Syntax:
if (expression):
statement1
statement2
.
.
statement...n
—
Some Important Points:
§
Python does not use { } to define the body of a code block, rather
it uses indentation.
§
A code block starts with indentation and
ends with the first unindented line.
§
The amount of indentation is up to the programmer, but he/she must be
consistent throughout that block.
§
The colon after if( ) condition is important and is a part of
the syntax. However, parenthesis with the condition is optional
The if – else Statement
—
The if … else statement evaluates test
expression and will execute the body of if only when
the test condition is True.
—
If the condition is False, the body of else is
executed.
—
Indentation is used to separate the blocks.
—
Syntax:
if (expression):
statement 1
statement 2
else:
statement 3
statement 4
Indentation and colon are important for else also
The if – elif - else Statement
—
The elif is short for else if. It allows us to
check for multiple expressions.
—
If the condition for if is False, it checks
the condition of the next elif block and so on.
—
If all the conditions are False, the body of else is
executed.
—
Syntax:
if (expression):
statement 1
statement 2
elif (expression):
statement 3
statement 4
else:
statement 5
statement 6
Although it is not visible in the syntax, but we can have multiple
elif blocks with a single if block.
The nested if Statement
—
We can have an if...elif...else statement inside
another if...elif...else statement.
—
This is called nesting in computer programming.
—
Any number of these statements can be nested inside one another.
Indentation is the only way to figure out the level of nesting
—
Syntax:
if (expression):
if (expression):
statement 1
statement 2
else:
statement 3
statement 4
statement 5
statement 6
Assignment
—
Whether a number is even or odd.
—
WAP to accept a character from the user and check whether it is a capital
letter or a small letter. Assume user will input only alphabets.
—
WAP to accept a character from the user and check whether it is a capital
letter or small letter or a digit or some special symbol
—
WAP to accept 3 integers from the user and without using any logical
operator and cascading of relational operators, find out the greatest number
amongst them
—
WAP to accept a year from the user and check whether it is a leap year or
not.
A year is a leap year if:
It is exactly divisible by 4 AND at the same time
not divisible by
100
OR
it is divisible by 400
For example:
2017 is not a leap year
2012 is a leap year
1900 is a not leap year
2000 is a leap year
If you have any doubt regarding this topic then, you can ask your doubt in
the comment section, I will respond to you as soon as possible.
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