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C++ Program to Find the Reverse of a Number

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reverse of a number

C++ program to find the reverse of a number has been shown here. For example, if a number is 12345 then the reverse of the number is 54321. The following section covers both of the iterative and recursive approaches to find the reverse of a number. The algorithm, pseudocode and time complexity of the program have been shown below.






1. Algorithm to find reverse of a number


1. Take a number n as input.

2. Initialize a variable to 0 say reverse = 0.

3. Perform r = n % 10.

4. Perform reverse = reverse * 10 + r.

5. Perform n = n / 10

6. If n = 0 stop the process and display reverse as output else go to step 3.




2. Pseudocode to find reverse of a number


Input : A number $n$

Output : The reverse of the number $n$

1. Procedure reverse($n$):

2. $reverse \leftarrow 0$

3. Repeat until $n != 0$

4. $reverse \leftarrow reverse * 10 + (n \mod 10)$

5. $n \leftarrow n / 10$

6. Return $reverse$

7. End Procedure





3. Time complexity to find reverse of a number


Time Complexity: O(log(n))

Where n is the input number.





4. Program & output to find reverse of a number




4.1. C++ Program & output to find reverse of a number using iteration

Code has been copied
/*******************************
    alphabetacoder.com
C++ program to find the reverse
of a number using iteration
********************************/

#include <iostream>

using namespace std;

int main() {
    // declare variables
    int num, revnum = 0, r;

    // take input of the number
    cout << "Enter the number = ";
    cin >> num;

    //find the reverse
    while (num != 0) {
        // extract the unit digit
        r = num % 10;
        // store the reverse number.
        // provide appropriate positional value
        // of each digit in each iteration.
        revnum = revnum * 10 + r;
        //divide the number by 10
        num = num / 10;
    }

    // display result
    cout << "Reverse of the number = " << revnum << endl;

    return 0;
}

Output

Case 1:

Enter the number = 12345

Reverse of the number = 54321


Case 2:

Enter the number = 68421

Reverse of the number = 12486





4.2. C++ Program & output to find reverse of a number using recursion

Code has been copied
/*******************************
	alphabetacoder.com
C++ program to find the reverse
of a number using recursion
********************************/

#include <iostream>

using namespace std;

// recursive function to reverse a number
int reverse(int num, int rev) {
    if (num == 0)
        return rev;
    else
        return reverse(num / 10, (rev * 10 + num % 10));
}

int main() {
    // declare variables
    int num;

    // take input of the number
    cout << "Enter the number = ";
    cin >> num;

    //find the reverse by calling function
    // The function has two parameters.
    // First one is the number and second one
    // is for storing the reverse of a number
    // display the result
    cout << "Reverse of the number = " << reverse(num, 0) << endl;

    return 0;
}

Output

Case 1:

Enter the number = 63451

Reverse of the number = 15436


Case 2:

Enter the number = 9

Reverse of the number = 9





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