TCS Coding Practice Question | Reverse a Number

Difficulty Level : Medium
Last Updated : 22 Jul, 2019

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 <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.");
    }
}

Output:

In C:
In Java:

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