Reverse a number in C.

**Problem Statement:** Given a number N reverse the number and print it.

**Examples:**

Example 1:Input:N = 123Output:321Explanation:The reverse of 123 is 321Example 2:Input:N = 234Output:432Explanation:The reverse of 234 is 432

** Disclaimer**:

*Don’t jump directly to the solution, try it out yourself first.*

The idea is to extract digits from end of the given number and create a new number in reverse order.

**How to extract digits from end of a number?**

To extract the last digit, if you divide a number by 10, then the remainder will be the last digit. We can simply use the modulo(%) operator to do this, example: last digit of 123 will be (123 % 10), which is 3.

To reduce number by one digit from end, simply divide the number by 10. example: to reduce 123 to 12, simply do (123/10) which is equals to 12.

**To create a number from digits:** The idea is to start with 0, and for every digit, multiply the number generated so far by 10, and add the digit to it.

For example, to create a number from digits: [1,2,3]:

Consider the number, num = 0.

Then,

For first digit: 1num = num*10 + 1 = 0*10 + 1 = 1;For second digit: 2num = num*10 + 2 = 1*10 + 2 = 12;For third digit:3 num = num*10 + 2 = 12*10 + 3 = 123;

**Approach:**

- Run a while loop until the given number N is equal to zero while(N!=0)
- Initialize a variable reverse = 0;
- now in each step take remainder of the given number N store it a variable digit, digit = N % 10
- Also Divide the number by 10. N= N / 10
- in each step the variable reverse get updated as reverse = reverse*10+digit.

**Code:**

## C Program

```
#include<stdio.h>
int main()
{
int N = 123;
int num = N;
int reverse = 0;
while(N!=0)
{
int digit = N%10;
reverse = reverse*10+digit;
N = N/10;
}
printf("The reverse of the %d is %d",num,reverse);
}
```

**Output:** The reverse of the 123 is 321

**Time Complexity:** O(n), where n is the length of the given number

**Space Complexity:** O(1)

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