Python: If-else statements

 If-else  in Python is one of the decision making statements, which is the most important aspect of almost all programming languages. Decision making allows us to run a particular block of codes for a particular decision. Decisions are based on the particular conditions. Condition checking is the backbone of decision making.

In Python decision making is performed by following statements:

Statement	Description
If Statement	The if statement is used to test a specific condition, if the condition is true, a block of code will be executed.
If-else Statement	The if-else statement is similar to if statement except the fact that it also executes the block of codes for false case of condition. If the condition provided will be false, the else statement will be executed.
Nested if Statement	Here more than one if-else statement is found. If condition matches then inner if statement is executed, otherwise outer (else) statement is executed.

The inner and outer if statements in Python are recognised by level of indentation. The statements written in same indentation level are recognised as one block of codes. Hence indentation is the most useful and unique part of Python because it declares the block of codes.

The if statement

The if condition is used to test a particular condition and if the condition is true, it executes the block of code, known as if-block. The condition of if statement may be any logical expression, which can either be evaluated or be true/false.

The syntax of the if-statement is given below:

if expression: statement

Example1:

num = int(input("Enter the number:")) if num%2==0:     print("The given number is an even number")

Output

Enter the number:   The given number is an even number

Example2: Program to print largest of the three numbers

a = int(input("Enter a:")) b = int(input("Enter b:")) c = int(input("Enter c:")) if a>b and a>c:     print("Here a is the largest number") if b>a and b>c:     print("Here b is the largest number") if c>b and c>a:     print("Here c is the largest number")

Output

Enter a: 100 Enter b: 90 Enter c: 170 Here c is the largest number

The if-else statement

The if-else statement gives another block of codes, the else block of codes with if block of codes. It is executed in false case of if statements.

Syntax of the if else statement is given below:

if condition:     #block of statements else:     #another block of statements (else block)

Example1: Program to check whether a person is eligible to vote or not.

age=int(input("Enter your age:")) #if block of statement if age>=18:     print("You are eligible to vote") #else block of statement else:     print("Sorry! you should wait")

Output

Enter your age: 19 You are eligible to vote

Example2: Program to check whether a numbder is odd or even.

num=int(input("Enter any number:")) #if block of statement if num%2==0:     print("The number is even") #else block of statement else:     print("The number is odd")

Output

Enter any number: 19 The number is odd

The elif statement

The elif statement enables us to check multiple conditions and executes the specific block of statements depending upon the true condition among them. We can have any number of elif statement in our program depending upon our need. However, using elif is optional.

The elif statement in Python works like if-else-if ladder statement in C. It must be succeeded by an if statement.

Syntax of elif statement:

if expression1:     #block of styatements elif expression 2:     #block of styatements elif expression3:     #block of styatements else:     #block of styatements

Example 1:

num=int(input("enter the num:")) if num%7==0:      print("The number is multiple of 7") elif num%10==0:     print("The number is multiple of 5 and 10"); elif num%9==0:     print("The number is multiple of 3 and 9"); else:     print("The number is not multiple of 5, 9 and 10");

Output

enter the num: 81 The number is multiple of 3 and 9

Example 2: Simple Python program to calculate grades.

marks=int(input("enter the marks:")) if marks>89 and marks<=100:      print("Congrates! You scored Grade A") elif marks>74 and marks<=89:     print("You scored Grade B"); elif marks>59 and marks<=74:     print("You scored Grade C"); elif marks>44 and marks<=59:     print("You scored Grade D"); elif marks>32 and marks<=44:     print("You scored Grade E"); else:     print("Sorry! You are fail");

Output

enter the marks: 56 You scored Grade D