C Program to Reverse a Number

In programming, we can display the reversed number by printing all its digits from the rightmost digit to the left-most integer. But, to retain it as a number, we apply some math to store the value at each iteration.

Algorithm to Reverse a Number in C

1. Initialize rev_num to 0 // variable to hold the reverse of a number in c
2. While num > 0 // Loop until there are no more digits in num a. Extract the last digit of num: digit = num % 10 b. Append digit to rev_num: rev_num = rev_num * 10 + digit c. Remove the last digit from num: num = num / 10
3. Return rev_num // rev_num now contains the reversed number

C Program to Reverse a Number in C

Using While Loop

Code:

Output:

Explanation: Let's break down the operation of the while loop for the given reverse number program in c, input number n is 12345.

Finally, reversed_number, now holding the reversed sequence of digits, is displayed as output.

Complexity Analysis

Time complexity: $O(n)$ Space complexity: $O(1)$

Using Recursion

Code:

Output:

Explanation: The function reverse_number explains how to reverse a number in c using recursive calls, shrinking number by a factor of 10 each time, and accumulates the reversed number using the remainder.

Complexity Analysis

Time complexity: $O(n)$
Space complexity: $O(n)$ ,due to recursive call stack

Using For Loop

Code:

Output:

Explanation: The code uses a for loop to iterate through digits of number, extracting and appending each digit to reversed_number until i becomes 0.

Complexity Analysis

Time complexity: $O(n)$
Space complexity: $O(1)$

Using Function

Code:

Output:

Explanation: In this approach, the reverse_number function reverses the input number by repeatedly extracting its last digit and building the reversed_number in a while loop.

Complexity Analysis

Time complexity: $O(n)$
Space complexity: $O(1)$

Flow of the Program to Reverse a Number in C

See Also

• C Program to Reverse an Array
• Reverse a String in C
• Reverse a Number in C++
• Reverse a Number in Javascript