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As it must be clear by the name, in the nested if-else decision-making statement, the if-else statement is nested inside the if statement(a parent condition), hence the nested if-else statement is termed as the nested if-else.

Working of nested if-else

• First, the condition of the parent if statement is evaluated for a boolean value - true or false.


• If the condition of the parent if statement is true, then the condition of the nested if statement is evaluated.
  
  
• In that case, if the condition of nested if statement is true, then the statement or a block of statements connected to it is executed.


• But, if the condition of the nested if is evaluated to be false, then the statement or a block of statements connected to its associated else statement is executed.


• If the condition of the parent if statement is false then the statement connected to its optional else statement(if declared) is executed and the nested if-else is not executed at all.











Important points about conditional statements in Python



• As you can see in the diagram above, In Python, a colon: is required after declaring the condition of a conditional statement, be it an if, else, etc, which helps us in declaring the start of an upcoming indented block and it also improves readability.


• In Python, the condition of an if, elif statement can even be declared without a pair of parentheses () around it(contrary to many programming languages like C, C++ which require us to wrap a condition within a pair of parentheses).


• Unlike many programming languages like C, C++, Java which require a pair of braces { } to hold multiple statements associated with a conditional statement like if, else, etc, the Python language does not require you to use a pair of braces { } to contain one or more statements with any conditional statement.


• Using a pair of braces { } to hold one or more statements with any conditional statement like if or else statement gives an error.


• Then how do we associate one or multiple statements with a conditional statement like if, elif or else?
  In Python, indentation is meaningful and using it we can associate one or more statements with any conditional statement.





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Nested if-else example




# Python - nested if-else example

if(99<100):
	if(99<98):		#nested if-else statement
		print("99 is less than 100 & 99 is also less than 101")
	else:
		print("99 is less than 100 but 99 is not less than 98")
else:
	print("99 is not less than 100")





Output




99 is less than 100 but 99 is not less than 98





Program Analysis



• The parent if statement condition i.e. 99<100 is true, hence its associated nested if-else statement is evaluated.
• Because the condition of nested if statement is evaluated to be false, therefore its associated else statement, is executed and the message 99 is less than 100 but 99 is not less than 98 is printed.






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