Learn Python – Python If-else statements- Basic and advance

Decision making is the most vital element of nearly all the programming languages. As the title implies, selection making permits us to run a particular block of code for a precise decision. Here, the choices are made on the validity of the unique conditions. Condition checking is the backbone of selection making.

In python, choice making is carried out via the 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 (if-block) will be executed.
If – else Statement The if-else statement is similar to if statement except the fact that, it also provides the block of the code for the false case of the condition to be checked. If the condition provided in the if statement is false, then the else statement will be executed.
Nested if Statement Nested if statements enable us to use if ? else statement inside an outer if statement.

Indentation in Python

For the ease of programming and to reap simplicity, python would not enable the use of parentheses for the block level code. In Python, indentation is used to declare a block. If two statements are at the equal indentation level, then they are the part of the equal block.

Generally, four spaces are given to indent the statements which are a normal quantity of indentation in python.

Indentation is the most used section of the python language for the reason that it proclaims the block of code. All the statements of one block are intended at the equal degree indentation. We will see how the actual indentation takes vicinity in choice making and other stuff in python.

The if statement

The if announcement is used to test a specific situation and if the condition is true, it executes a block of code recognized as if-block. The circumstance of if assertion can be any valid logical expression which can be either evaluated to actual or false.

The syntax of the if-statement is given below.

if expression:  
    statement  

Example 1

num = int(input("enter the number?"))  
if num%2 == 0:  
    print("Number is even")  

Output:

enter the number?10
Number is even

Example two : Program to print the greatest 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("a is largest");  
if b>a and b>c:  
    print("b is largest");  
if c>a and c>b:  
    print("c is largest");  

Output:

Enter a? 100
Enter b? 120
Enter c? 130
c is largest

The if-else statement

The if-else announcement gives an else block combined with the if statement which is achieved in the false case of the condition.

If the situation is true, then the if-block is executed. Otherwise, the else-block is executed.

The syntax of the if-else statement is given below.

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

Example 1 : Program to test whether a person is eligible to vote or not.

age = int (input("Enter your age? "))  
if age>=18:  
    print("You are eligible to vote !!");  
else:  
    print("Sorry! you have to wait !!");  

Output:

Enter your age? 90
You are eligible to vote !!

Example 2: Program to check whether a quantity is even or not.

num = int(input("enter the number?"))  
if num%2 == 0:  
    print("Number is even...")  
else:  
    print("Number is odd...")  

Output:

enter the number?10
Number is even

The elif statement

The elif declaration allows us to check multiple prerequisites and execute the precise block of statements relying upon the true situation amongst them. We can have any quantity of elif statements in our application depending upon our need. However, using elif is optional.

The elif declaration works like an if-else-if ladder announcement in C. It must be succeeded with the aid of an if statement.

The syntax of the elif statement is given below.

if expression 1:   
    # block of statements   
  
elif expression 2:   
    # block of statements   
  
elif expression 3:   
    # block of statements   
  
else:   
    # block of statements  

Example 1

number = int(input("Enter the number?"))  
if number==10:  
    print("number is equals to 10")  
elif number==50:  
    print("number is equal to 50");  
elif number==100:  
    print("number is equal to 100");  
else:  
    print("number is not equal to 10, 50 or 100");  

Output:

Enter the number?15
number is not equal to 10, 50 or 100

Example 2

marks = int(input("Enter the marks? "))  
f marks > 85 and marks <= 100:  
   print("Congrats ! you scored grade A ...")  
lif marks > 60 and marks <= 85:  
   print("You scored grade B + ...")  
lif marks > 40 and marks <= 60:  
   print("You scored grade B ...")  
lif (marks > 30 and marks <= 40):  
   print("You scored grade C ...")  
lse:  
   print("Sorry you are fail ?")