TCS Coding Practice Question | Reverse a Number

Given a number, the task is to reverse this number using Command Line Arguments. Examples:

Input: num = 12345
Output: 54321

Input: num = 786
Output: 687

Approach:

• Since the number is entered as Command line Argument, there is no need for a dedicated input line
• Extract the input number from the command line argument
• This extracted number will be in String type.
• Convert this number into integer type and store it in a variable, say num
• Initialize a variable, say rev_num, to store the reverse of this number with 0
• Now loop through the number num till it becomes 0, i.e. (num > 0)
• In each iteration,
  • Multiply rev_num by 10 and add remainder of num to it. This will store the last digit of num in rev_num
  • Divide num by 10 to remove the last digit from it.
• After the loop has ended, rev_num has the reverse of num.

Program:

C++

// C++ program to reverse a number
// using command line arguments

#include <iostream>
#include <string>
#include <sstream>
using namespace std;

// Function to reverse the number
int reverseNumber(int num)
{

    // Variable to store the
    // resultant reverse number
    int rev_num = 0;

    // Traverse through the number digit by digit
    while (num > 0) {

        // Append the last digit of num
        // as the next digit of rev_num
        rev_num = rev_num * 10 + num % 10;

        // Remove the last digit from the num
        num = num / 10;
    }

    // Return the reversed number
    return rev_num;
}

// Driver code
int main(int argc, char* argv[])
{

    int num;

    // Check if the length of args array is 1
    if (argc == 1)
        cout << "No command line arguments found.\n";
    else {

        // Get the command line argument and
        // Convert it from string type to integer type
        // using function "atoi( argument)"
        num = atoi(argv[1]);

        // Reverse the number and print it
        cout << reverseNumber(num) << endl;
    }
    return 0;
}

C

// C program to reverse a number
// using command line arguments

#include <stdio.h>
#include <stdlib.h>     /* atoi */

// Function to reverse the number
int reverseNumber(int num)
{

    // Variable to store the
    // resultant reverse number
    int rev_num = 0;

    // Traverse through the number digit by digit
    while (num > 0) {

        // Append the last digit of num
        // as the next digit of rev_num
        rev_num = rev_num * 10 + num % 10;

        // Remove the last digit from the num
        num = num / 10;
    }

    // Return the reversed number
    return rev_num;
}

// Driver code
int main(int argc, char* argv[])
{

    int num;

    // Check if the length of args array is 1
    if (argc == 1)
        printf("No command line arguments found.\n");
    else {

        // Get the command line argument and
        // Convert it from string type to integer type
        // using function "atoi( argument)"
        num = atoi(argv[1]);

        // Reverse the number and print it
        printf("%d\n", reverseNumber(num));
    }
    return 0;
}

Java

// Java program to reverse a number
// using command line arguments

class GFG {

    // Function to reverse the number
    public static int reverseNumber(int num)
    {

        // Variable to store the
        // resultant reverse number
        int rev_num = 0;

        // Traverse through the number digit by digit
        while (num > 0) {

            // Append the last digit of num
            // as the next digit of rev_num
            rev_num = rev_num * 10 + num % 10;

            // Remove the last digit from the num
            num = num / 10;
        }

        // Return the reversed number
        return rev_num;
    }

    // Driver code
    public static void main(String[] args)
    {

        // Check if length of args array is
        // greater than 0
        if (args.length > 0) {

            // Get the command line argument and
            // Convert it from string type to integer type
            int num = Integer.parseInt(args[0]);

            // Reverse the number and print it
            System.out.println(reverseNumber(num));
        }
        else
            System.out.println("No command line "
                               + "arguments found.");
    }
}

Python

import sys

# Function to reverse the number
def reverseNumber(num):
    # Variable to store the resultant reverse number
    rev_num = 0

    # Traverse through the number digit by digit
    while num > 0:
        # Append the last digit of num as the next digit of rev_num
        rev_num = rev_num * 10 + num % 10

        # Remove the last digit from the num
        num = num // 10

    # Return the reversed number
    return rev_num

# Driver code
if __name__ == "__main__":
    if len(sys.argv) == 1:
        print("No command line arguments found.")
    else:
        # Get the command line argument and convert it from string to integer
        num = int(sys.argv[1])

        # Reverse the number and print it
        print(reverseNumber(num))

Output:

• In C:

• In Java :

• In Python

• In C++: