# Define an empty list to store tasks
tasks = []

# Define a function to add tasks to the list
def add_task():
    task = input("Enter the task description: ")
    tasks.append(task)
    print("Task added successfully!")

# Define a function to display the list of tasks
def display_tasks():
    if not tasks:
        print("No tasks found!")
    else:
        print("Task List:")
        for i, task in enumerate(tasks, start=1):
            print(f"{i}. {task}")

# Define a function to mark tasks as completed
def complete_task():
    display_tasks()
    if not tasks:
        return

    try:
        task_index = int(input("Enter the task number to mark as completed: "))
        if 1 <= task_index <= len(tasks):
            completed_task = tasks.pop(task_index - 1)
            print(f"Task '{completed_task}' marked as completed!")
        else:
            print("Invalid task number! Please enter a valid task number.")
    except ValueError:
        print("Invalid input! Please enter a number.")

# Define a function to update task descriptions
def update_task():
    display_tasks()
    if not tasks:
        return

    try:
        task_index = int(input("Enter the task number to update: "))
        if 1 <= task_index <= len(tasks):
            new_task = input("Enter the new task description: ")
            tasks[task_index - 1] = new_task
            print("Task updated successfully!")
        else:
            print("Invalid task number! Please enter a valid task number.")
    except ValueError:
        print("Invalid input! Please enter a number.")

# Define a function to remove tasks from the list
def remove_task():
    display_tasks()
    if not tasks:
        return

    try:
        task_index = int(input("Enter the task number to remove: "))
        if 1 <= task_index <= len(tasks):
            removed_task = tasks.pop(task_index - 1)
            print(f"Task '{removed_task}' removed successfully!")
        else:
            print("Invalid task number! Please enter a valid task number.")
    except ValueError:
        print("Invalid input! Please enter a number.")

# Define a function to display the menu of options
def display_menu():
    print("To-Do List Application")
    print("---------------------")
    print("1. Add Task")
    print("2. Display Tasks")
    print("3. Mark Task as Completed")
    print("4. Update Task")
    print("5. Remove Task")
    print("6. Exit")

# Define the main function to run the application
def main():
    while True:
        display_menu()
        try:
            choice = int(input("Enter your choice: "))
            if choice == 1:
                add_task()
            elif choice == 2:
                display_tasks()
            elif choice == 3:
                complete_task()
            elif choice == 4:
                update_task()
            elif choice == 5:
                remove_task()
            elif choice == 6:
                print("Exiting...")
                break
            else:
                print("Invalid choice! Please enter a number between 1 and 6.")
        except ValueError:
            print("Invalid input! Please enter a number.")

if __name__ == "__main__":
    main()