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Swap Two Numbers (With Temporary Variable)

Learning Objectives

By the end of this tutorial, you will be able to: - Understand the concept of using a temporary variable for swapping values - Implement swapping algorithms in Java, Python, C, and Oracle PL/SQL - Analyze the time and space complexity of the swapping process - Apply swapping techniques to real-world programming scenarios - Debug common issues that occur during variable swapping

Concept Explanation

What is it?

Swapping two numbers or values means exchanging their content. For example, if variable A holds 10 and variable B holds 20, after swapping, A will hold 20 and B will hold 10. One common method to achieve this is by using a third, temporary variable to hold one of the values during the exchange process.

Why is it important?

Swapping values is a fundamental operation in computer programming. It's used in many algorithms such as sorting (e.g., bubble sort), array manipulations, and various data structure operations where the order or position of elements needs to be changed.

Where is it used?

  • Sorting Algorithms: Many algorithms, like bubble sort or selection sort, rely on repeatedly swapping elements.
  • Array/List Reversal: Reversing the order of elements in a data structure.
  • Data Encryption: Certain cryptographic algorithms might involve swapping bits or bytes.
  • Game Development: Swapping positions of game objects or character attributes.

Real-world example

Imagine two people, Alice and Bob, each holding a different book. If they want to exchange books, they might need a third person (like a librarian) to temporarily hold one book while the exchange happens. Alice gives her book to the librarian, Bob gives his book to Alice, and then the librarian gives Alice's original book to Bob.

Algorithm

  1. Start.
  2. Get two numbers, num1 and num2, from the user.
  3. Declare a temporary variable, temp.
  4. Store the value of num1 into temp (temp = num1).
  5. Assign the value of num2 to num1 (num1 = num2).
  6. Assign the value of temp to num2 (num2 = temp).
  7. Display the swapped values of num1 and num2.
  8. End.

Edge Cases: - Inputting non-numeric values (handled by language-specific error mechanisms or explicit validation). - Swapping identical numbers will result in no change, which is correct behavior.

Implementations

import java.util.Scanner;

public class SwapNumbersWithTemp {
    public static void main(String[] args) {
        Scanner scanner = new Scanner(System.in);

        System.out.print("Enter the first number (num1): ");
        int num1 = scanner.nextInt();

        System.out.print("Enter the second number (num2): ");
        int num2 = scanner.nextInt();

        System.out.println("Before swapping:");
        System.out.println("num1 = " + num1);
        System.out.println("num2 = " + num2);

        // Swapping logic using a temporary variable
        int temp = num1;
        num1 = num2;
        num2 = temp;

        System.out.println("After swapping:");
        System.out.println("num1 = " + num1);
        System.out.println("num2 = " + num2);

        scanner.close();
    }
}

# Get two numbers from the user
num1_str = input("Enter the first number (num1): ")
num1 = float(num1_str)

num2_str = input("Enter the second number (num2): ")
num2 = float(num2_str)

print(f"Before swapping:")
print(f"num1 = {num1}")
print(f"num2 = {num2}")

# Swapping logic using a temporary variable
temp = num1
num1 = num2
num2 = temp

print(f"After swapping:")
print(f"num1 = {num1}")
print(f"num2 = {num2}")

#include <stdio.h>

int main() {
    int num1, num2;
    int temp; // Temporary variable for swapping

    printf("Enter the first number (num1): ");
    scanf("%d", &num1);

    printf("Enter the second number (num2): ");
    scanf("%d", &num2);

    printf("Before swapping:\n");
    printf("num1 = %d\n", num1);
    printf("num2 = %d\n", num2);

    // Swapping logic
    temp = num1;
    num1 = num2;
    num2 = temp;

    printf("After swapping:\n");
    printf("num1 = %d\n", num1);
    printf("num2 = %d\n", num2);

    return 0;
}

SET SERVEROUTPUT ON;
DECLARE
  num1        NUMBER := &Enter_First_Number;
  num2        NUMBER := &Enter_Second_Number;
  temp_var    NUMBER; -- Temporary variable for swapping
BEGIN
  DBMS_OUTPUT.PUT_LINE('Before swapping:');
  DBMS_OUTPUT.PUT_LINE('Num1: ' || num1);
  DBMS_OUTPUT.PUT_LINE('Num2: ' || num2);

  -- Swapping logic
  temp_var := num1;
  num1 := num2;
  num2 := temp_var;

  DBMS_OUTPUT.PUT_LINE('After swapping:');
  DBMS_OUTPUT.PUT_LINE('Num1: ' || num1);
  DBMS_OUTPUT.PUT_LINE('Num2: ' || num2);
END;
/

Explanation

  • Java: Uses a temp integer variable to facilitate the swap. Scanner is used for input.
  • Python: Similarly uses a temp variable. Note that Python offers a more concise way to swap (num1, num2 = num2, num1), but this implementation uses a temporary variable for conceptual clarity.
  • C: Requires a temp integer variable. scanf() is used to read input, and printf() to display.
  • Oracle: Implemented in PL/SQL. A NUMBER variable temp_var is declared to hold the value temporarily. Substitution variables are used for interactive input.

Complexity Analysis

  • Time Complexity: O(1) - The number of operations is constant, regardless of the values being swapped.
  • Space Complexity: O(1) - Only a single additional temporary variable is used.

Flowchart

graph TD
    A[Start] --> B[Get num1]
    B --> C[Get num2]
    C --> D[Declare temp]
    D --> E[temp = num1]
    E --> F[num1 = num2]
    F --> G[num2 = temp]
    G --> H[Display num1, num2]
    H --> I[End]

Sample Dry Run

Step num1 num2 temp Description
Initial 5 10 - Variables initialized
temp = num1 5 10 5 num1's value saved in temp
num1 = num2 10 10 5 num1 gets num2's value
num2 = temp 10 5 5 num2 gets original num1's value
Final 10 5 5 Values are swapped

Practice Problems

Easy

  • Modify the program to swap three numbers (e.g., A to B, B to C, C to A).
  • Swap two characters instead of numbers.

Medium

  • Implement swapping without using a temporary variable (using arithmetic or bitwise operations).
  • Swap elements in an array at specified indices.

Hard

  • Implement a generic swap function/method that works with different data types (where applicable by language).

Interactive Elements

Try It Yourself

Quick Test

  1. What will be the output if we swap the values 15 and 25 using a temporary variable?
  2. Modify the program to swap three numbers in sequence (A→B, B→C, C→A)
  3. Create a function that swaps two variables and returns the swapped values

Code Challenge

Write a program that: - Takes two numbers as input - Swaps them using a temporary variable - Displays the original and swapped values - Includes error handling for non-numeric input

Learning Path

Before This Tutorial

After This Tutorial

Interview Tips

  • Explain the Logic: Clearly describe why a temporary variable is needed for swapping
  • Mention Complexity: State that it's O(1) time and O(1) space complexity
  • Discuss Edge Cases: Talk about swapping identical numbers or zero values
  • Real-world Applications: Mention sorting algorithms and data structures
  • Alternative Methods: Briefly mention that there are ways to swap without temporary variables

Best Practices & Common Mistakes

General Programming Principles

Language-Specific Guidance

Concept-Specific Considerations

  • Variables and Assignment: Understanding how values are stored and transferred
  • Memory Management: How temporary variables use memory
  • Control Structures: Sequential execution of statements
  • Data Types: Working with different numeric types
  • Algorithm Design: Basic building blocks of larger algorithms
  • Sorting Algorithms: Where swapping is frequently used

"Programming is not about typing, it's about thinking." - Rich Hickey