# Reverse a Number in Python Using For Loop

(Last Updated On: 26/09/2023)

We often necessary to manipulate and transform data to suit specific requirements while programming. One such operation is reversing a number, where the digits of a given number are rearranged in reverse order. Reversing a number can be a useful technique in various scenarios, such as data analysis, algorithmic problem-solving, or cryptography.

In this blog, we will explore how to reverse a number in Python using for loop. We will also discuss step-by-step and detailed explanations of the code involved. This blog will give you a solid understanding of how to reverse a number using a for loop in Python and be able to apply this knowledge to your own programming projects.

So, let’s dive into the Python program to reverse a number using for loop and learn how to manipulate and reverse numbers efficiently.

## Python Program to Reverse a Number Using For Loop

```# Reverse a Number in Python Using For Loop

# we are taking a number from user as input
num = input("Enter the first number:")

# calculate reverse of number
reverse = ''
for i in range(len(num), 0, -1):
reverse += num[i-1]

# print reverse of number
print('The reverse number is =', reverse)
```

#### Code Logic Explanation

• Accepting the number from the user

The first step is to prompt the user to enter a number using the input() function which is stored as a string in the variable num.

• Calculating the reverse of the number

In this step, we will Initialise an empty string variable called reverse to store the reversed number.

• Iterating through the digits of the number

Next, we use a for loop to iterate through each digit of the number. The loop iterates over a range starting from the length of the number and going down to 1. Inside the loop, the current digit is accessed using num[i-1], where i is the loop variable. Since indexing starts from 0, we subtract 1 from i. Then it appends the current digit to the reverse string using the += operator.

• Displaying the reverse of the number

After the for loop completes, the reversed number is stored in the reverse variable. Using the print() function we display the reversed number concatenated with the string ‘The reverse number is =’.

#### Output:

``````Enter the first number:12356
The reverse number is = 65321``````

In this example, the user enters the number 12345. The program then reverses the digits of the number using a for loop. The reversed number is 54321. The program displays the reversed number with the message “The reverse number is = 54321”.

In this program, we prompt the user to enter a number (‘123456’), which is then stored as a string in the variable ‘num’ and initialise the ‘reverse’ variable as an empty string. The ‘for’ loop iterates through the length of the ‘num’ string in reverse order, starting from the last index and ending at the first index.

In each iteration, the current character at the index is added to the ‘reverse’ variable using the ‘+=’ operator. Finally, the reversed string is printed as output: ‘654321’.

### Multiple ways to reverse a number in Python

There are multiple ways to reverse a number in Python. Besides using a for loop, you can also use string slicing, recursion, or mathematical operations for reassembling the digits.

We can use the for loop method as it offers simplicity and readability. It is straightforward to understand and implement, making it suitable for beginners or situations where code readability is important. It provides a clear step-by-step iteration through the digits of the number, adding them to the reverse variable. Additionally, this method does not require complex mathematical operations or recursive function calls, making it efficient and easier to debug. It strikes a good balance between simplicity and efficiency for reversing a number.

However, if you are dealing with large numbers, the mathematical operations or recursive approach might be more suitable. It’s important to consider factors like code complexity, maintainability, and performance when choosing the method for reversing a number in Python.

In this exercise, we have learned how to reverse a number in Python using a for loop. We clarified each step of the code in detail, making it simple for beginners to understand. Reversing a number may be a common operation in programming that has various applications in different areas.

### Some FAQs on reversing a number

Can this code be used to reverse numbers with decimal places?

No, this code is designed to reverse integers. If you need to reverse numbers with decimal places, additional modifications would be required to handle the fractional part separately.

Are there alternative approaches to reverse a number in Python?

Yes, alternative approaches include converting the number to a string, using slicing or the reversed() function to reverse the string representation, and converting it back to an integer.

How does the loop append digits to the reverse variable?

Explanation: Inside the for loop, the current digit is accessed using num[i-1] and appended to the reverse string using the += operator. This concatenates the current digit to the existing reversed number.

What is the purpose of the range() function in the for loop?

The range() function is used to generate a sequence of numbers to iterate over. In the code, range() is used to generate a sequence of numbers starting from the length of the input number and decrementing by 1 until it reaches 0.

What is the maximum number that can be reversed using this code?

The maximum number that can be reversed using this code is limited by the maximum size of a string in Python. In most implementations, this is approximately 536,870,912 characters.