CONDITIONAL STATEMENT IN PYTHON

CONDITIONAL STATEMENT IN PYTHON

Python if else statement

The if...else statement is the decision statement. it make the decision on basis of given condition for that it uses comparison operators.


Comparison Operator
These operators are used to compare values.

Operator	Description	Example
>	Greater than	x > y
<	Less than	x < y
==	Equal to	x == y
!=	Not equal to	x != y
>=	Greater than or equal to	x >= y
<=	Less than or equal to	x <= y

Logical Operator
These operators are used to compare multiple conditions.

Operator	Description	Example
and	True if both the operands are true	x and y
or	True if either of the operands is true	x or y
not	True if operand is false	not x

Python if statement

The if statement is used to test a condition. If the condition is true then a single statement or a block of statements is executed.

Flow Chart of 'If' Statement

Python if statement syntax

if  condition :        statement(s)

Note: The format() method returns the formatted string. The curly brackets {} are used to define placeholders for the arguments to be placed. In the example bellow, {0} is placeholder for "num" variable.

Example 1 : Check the entered number is positive

Logic
If a number is greater than or equal to zero then it is a positive number – (if the number>=0)
If a number is less than or equal to zero then it is a Negative number – (if the number<=0)

Coding

# input() to accept user input num = int (input ("Enter a number:")) #Check the value in num is greater than or equal to 0 if (num>=0) :      print("The {0} is positive number" .format(num))

Output

Enter a number: 10 The 10 is positive number

 

Python if else statement

The if else is a bi-directional conditional control statement. if statement is used to test a condition, if the condition is true then statements of if block will executed, otherwise, the else block will be executed.

Flow Chart of 'If..Else' Statement

Python if else syntax

if  condition :        statement(s) else :        statement(s)

Example 2: Check if a number is odd or even in python

Logic
When input is divided by 2 and leaves a remainder 0 then it is a even number.
When input is divided by 2 and leaves any remainder other than 0 then it is a odd number.

Coding

# input() to accept user input num = int(input("Enter a number: "))  #Check if the value of num is divisible by 2 if (num % 2) == 0:      print("{0} is Even number".format(num))   else:      print("{0} is Odd number".format(num))

Output

Enter a number: 9 9 is Odd number

Python elif statement

The elif statement allows us to check for multiple conditions. Here each condition is checked, and when a condition is found to be true, the statements corresponding to that condition are executed, and the control comes out of the structure without checking remaining conditions. If none of the conditions is true then the block of last else statement will executed.

Flow Chart of 'If..Elif' Statement

Python elif syntax

if  condition 1 :        statement(s) elif  condition 2 :        statement(s) elif  condition 3 :        statement(s) else :        statement(s)

Example 3: Check if a number is positive, negative and zero

Logic

If a number is greater than zero then it is a positive number – (if the number>0)

If a number is less than zero then it is a Negative number – (if the number<0)

Otherwise the  number is zero. 

Coding

# input() to accept user input num = int(input("Enter a number: "))       if (num > 0):      print("{0} is a positive number".format(num)) elif (num < 0):      print("{0} is a negative number".format(num))  else:      print("{0} is zero".format(num))

  


Output

Enter a number: -1 -1 is a negative number

 

Python nested if else statement

You can nest if statements inside another if statements.

Flow Chart of 'Nested If..Else' Statement

Python nested if else syntax

if condition 1:     if condition 2:         statement(s)     else:         statement(s) else:     statement(s)

Example 4: Check a year is leap year in python
Logic 

The year should be divisible by 4 and if it is divisible by 100 then also divisible by 400.

Coding

# input() to accept user input year = int(input("Enter a year: "))      if (year % 4)==0:      if (year % 100)==0:          if(year % 400)==0:                     print("{0} is a leap year".format(year))         else:                     print("{0} is not a leap year".format(year))      else:              print("{0} is a leap year".format(year))  else:          print("{0} is not a leap year".format(year))

Output

Enter a year: 2019 2019 is not a leap year Enter a year: 2020 2020 is a leap year

Example 5: Check a year is leap year or not using logical operator

year=int(input("Enter a year:")) if(year%4==0 and year%100!=0 or year%400==0):     print("The year is a leap year!) else:     print("The year isn't a leap year!)