TCS Coding Practice Question | Reverse a String

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

Input: Geeks
Output: skeeG

Input: GeeksForGeeks
Output: skeeGroFskeeG

Approach 1: Using another String to store the reverse

• Since the string is entered as Command line Argument, there is no need for a dedicated input line
• Extract the input string from the command line argument
• Create a String to store the resultant reversed string, say reversedString
• Traverse through this String character by character using loop, in reverse order
• Now append each character into the resultant reversedString
• This is the required reversed string

Program:

C

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

#include <stdio.h>
#include <stdlib.h>
#include <string.h>

// Function to reverse the String
char* reverseString(char input[])
{

    // Get the length of the string
    int length = strlen(input);
    int i;

    // String to store the reverse
    char* reversedString
        = (char*)malloc(length * sizeof(char));

    // Loop through the string
    // character by character in reverse order
    // and store it into the resultant string
    for (i = length - 1; i >= 0; i--)
        reversedString[length - 1 - i] = input[i];

    // Return the reversed String
    return reversedString;
}

// Driver code
int main(int argc, char* argv[])
{
    // 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 reverse it
        printf("%s\n", reverseString(argv[1]));
    }
    return 0;
}

Java

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

class GFG {

    // Function to reverse the String
    public static String reverseString(String input)
    {

        // String to store the reverse
        String reversedString = "";

        // Loop through the string
        // character by character in reverse order
        // and store it into the resultant string
        for (int i = input.length() - 1; i >= 0; i--)
            reversedString += input.charAt(i);

        // Return the reversed String
        return reversedString;
    }

    // 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 reverse it
            System.out.println(reverseString(args[0]));
        }
        else
            System.out.println("No command line "
                               + "arguments found.");
    }
}

Python

# Python program to reverse a string
# using command line arguments

import sys

# Function to reverse the String
def reverseString(input_str):
    # Reversing the string using slicing
    reversed_str = input_str[::-1]
    return reversed_str

# Driver code
if __name__ == "__main__":
    # Check if command line argument is provided
    if len(sys.argv) == 1:
        print("No command line arguments found.")
    else:
        # Get the command line argument
        # and reverse it
        print(reverseString(sys.argv[1]))

Output:

• In C:
• In Java:

In Python

Approach 2: Without using another String to store the reverse

• Since the string is entered as Command line Argument, there is no need for a dedicated input line
• Extract the input string from the command line argument
• Traverse through this String character by character using loop till half the length of the string
• Swap the characters from one end with the characters from the other end
• This is the required reversed string

Program:

C

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

#include <stdio.h>
#include <stdlib.h>
#include <string.h>

// Function to reverse a string
char* reverseString(char str[])
{

    int n = strlen(str);
    int i;
    char temp;

    // Swap character starting from two
    // corners
    for (i = 0; i < n / 2; i++) {
        temp = str[i];
        str[i] = str[n - i - 1];
        str[n - i - 1] = temp;
    }

    return str;
}

// Driver code
int main(int argc, char* argv[])
{
    // 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 reverse it
        reverseString(argv[1]);

        // Print the reversed string
        printf("%s\n", argv[1]);
    }
    return 0;
}

Java

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

class GFG {

    // Function to reverse the String
    public static String reverseString(String str)
    {

        int n = str.length();
        char temp;

        // Swap character starting from two
        // corners
        for (int i = 0; i < n / 2; i++) {
            str = str.substring(0, i)
                  + str.charAt(n - i - 1)
                  + str.substring(i + 1, n - i - 1)
                  + str.charAt(i)
                  + str.substring(n - i);
        }

        return str;
    }

    // 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 reverse it
            System.out.println(reverseString(args[0]));
        }
        else
            System.out.println("No command line "
                               + "arguments found.");
    }
}

Output:

• In C:
• In Java: