Understanding the Power of `if-else` Statements in Python
Tags: beginners, programming, python, opensource
Published: 2024-01-17 11:50:11

# Understanding the Power of `if-else` Statements in Python 

## Introduction

In the world of programming, decision-making is a fundamental concept. Programs often need to perform different actions based on specific conditions. This is where conditional statements, such as `if-else` statements, come into play. In Python, the `if-else` statement is a powerful tool that allows developers to create dynamic and responsive code.

## Anatomy of the `if-else` Statement

The `if-else` statement in Python is a conditional statement that allows you to execute different blocks of code based on whether a certain condition is true or false. The basic syntax looks like this:

```python
if condition:
    # Code to be executed if the condition is true
else:
    # Code to be executed if the condition is false
```

Let's break down the components:

- `if condition:`: This is the main condition that the program evaluates. If it is true, the code block inside the `if` statement is executed. Otherwise, the code block inside the `else` statement is executed.

- `else:`: This part is optional. If the condition specified in the `if` statement is false, the code inside the `else` block will be executed.

## Simple Examples

### Example 1: Checking if a Number is Even or Odd

```python
num = 7

if num % 2 == 0:
    print(f"{num} is even.")
else:
    print(f"{num} is odd.")
```

In this example, the program checks if the remainder of `num` divided by 2 is equal to 0. If it is, the number is even; otherwise, it's odd.

### Example 2: Determining the Sign of a Number

```python
number = -5

if number > 0:
    print(f"{number} is positive.")
elif number < 0:
    print(f"{number} is negative.")
else:
    print(f"{number} is zero.")
```

Here, the program checks whether a number is positive, negative, or zero using a combination of `if`, `elif` (else if), and `else` statements.

## Nested `if-else` Statements

In Python, you can nest `if-else` statements inside one another. This allows for more complex decision-making logic.

```python
x = 10

if x > 0:
    if x % 2 == 0:
        print(f"{x} is a positive even number.")
    else:
        print(f"{x} is a positive odd number.")
else:
    print(f"{x} is non-positive.")
```

In this example, the program first checks if `x` is positive. If it is, it further checks whether it's even or odd. If `x` is not positive, it prints that `x` is non-positive.

## Ternary Conditional Expression

Python also supports a concise version of the `if-else` statement known as the ternary conditional expression.

```python
result = "Even" if num % 2 == 0 else "Odd"
print(result)
```

This is equivalent to the first example but in a more compact form.

## Conclusion

The `if-else` statement in Python is a versatile tool that enables developers to create dynamic and flexible programs. Whether it's handling simple conditions or complex decision trees, understanding how to use `if-else` statements is crucial for any Python programmer. As you delve deeper into programming, you'll find that mastering conditional statements is a key step toward writing efficient and responsive code.

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## Question - 

1. Write a  Program to Check Whether a Number is Even or Odd.?
   
   ```yaml
   Enter Number to Find Even or odd = 3
    
   -- Your Number 3 is Odd 
   ```
2. Write a  Program to Check Whether an Alphabet is Vowel or Consonant ?

   ```yaml
   Enter Alphabet : A
    
   -- A is Vowel 
   ```
3. Write a  Program to Find the Largest Among Three Numbers ?
    
    ```yaml
    Enter Number 1 : 100
    Enter Number 2 : 300
    Enter Number 3 : 400 
    -- Number 300 is Largest 
    ```

4. Write a  Program to Check Leap Year ?

    ```yaml
   Enter Year : 2023 

   -- 2023 is not Leap Year 
   ```

5. Write a program to find Grade ?
   
   ```yaml
   Example : Grading System 
   80 - 100 = Grade A
   60 - 80 = Grade B
   40 - 60 = Grade C
   30 - 40 = Grade D
   0  - 30 Grade F

   ```

6. Find Age ?
   
   ```yaml
   -- Date of birth Section 

   Enter Your Birth Year : 1992
   Enter Your Birth Month : 4
   Enter Your Birth Day : 16

   -- Current Date

   Enter Your Current Year : 2023
   Enter Your Current Month : 7
   Enter Your Current Day : 26 

   -- output
   
   30 years 3 months 10 days
   or 363 months 10 days
   or 1579 weeks 5 days
   or 11,058 days
   or 265,392 hours
   
   ```

7. Password Checker 
Example : 
```yaml
   Set your password :
   p4n@in
   Enter your Password : 
   p4n
   wrong password ... try 2 more time out of 2
   p4n@
   wrong password ... try 1 more time 1
   p4n@34
   wrong password ... try 0 more time 0
   note : user select right password
   then start MCQ EXAM...
   
    
   1. Who invented Java Programming?
   1. ) Guido van Rossum
   2. ) James Gosling
   3. ) Dennis Ritchie
   4. ) Bjarne Stroustrup
   
   Select Answer 2
   
   wrong answer [ Try Next year ] 
   
   Note :if select Right Answer 
   ask 2nd Question ...
   
   2. Which component is used to compile, debug and execute the java programs?
   1. ) JRE
   2. ) JIT
   3. ) JDK
   4. ) JVM
   
   Select Answer 2 ... con..
```    

8. Student Report Card System
```Yaml
---- Input Section
Enter your name : Joy
Enter Your Roll Number : A1023

Enter Your JAVA Marks : 50
Enter Your C++ Marks : 20
Enter Your go Marks : 25
Enter Your Ruby Marks : 96
Enter Your C# Marks : 70
Enter Your Python Marks : 65

---- Output Section
JAVA = 50/100 
C++ = 20/100 F
go = 25/100 F
Ruby = 96/100
C# = 70/100
Python = 65/100

Total = 326/600
per = 54% FAIL
IF PASS
Grading System 
80 - 100 = Grade A
60 - 80 = Grade B
40 - 60 = Grade C
30 - 40 = Grade D
```