1. C Language Examples of Array Pointers, Pointer Arrays, Function Pointers, and Pointer Functions

Pointer Array

An array where each element is a pointer is called a pointer array.
int *ptr_arr[10];

#include <stdio.h>

int main() {
    int arr1[] = {1, 2, 3, 4, 5};
    int arr2[] = {6, 7, 8, 9, 0};
    int arr3[] = {1, 2, 3, 4, 5};

    int* ptr_arr[] = {arr1, arr2, arr3};

    for (int i = 0; i < 3; i++) {
        for (int j = 0; j < 5; j++) {
            printf("%d", *(ptr_arr[i] + j));
        }
        printf("\n");
    }

    return 0;
}

Array Pointer

An array pointer points to an array and stores its address.
int (*ptr)[10];

#include <stdio.h>

int main() {
    int matrix[3][4] = {0, 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11};
    int(*array_ptr)[4];
    array_ptr = matrix;

    for (int i = 0; i < 3; i++) {
        for (int j = 0; j < 4; j++) {
            printf("%2d   ", *(*(array_ptr + i) + j));
        }
        printf("\n");
    }

    return 0;
}

Function Pointer

A function pointer refers to a function.

#include <stdio.h>

int add(int a, int b) {
    return a + b;
}

int subtract(int a, int b) {
    return a - b;
}

int main() {
    int (*func_ptr)(int, int);

    func_ptr = add;
    printf("Addition: %d\n", func_ptr(1, 2));

    func_ptr = subtract;
    printf("Subtraction: %d\n", func_ptr(2, 1));

    return 0;
}

Pointer Function

A functon that returns a pointer to another function.

#include <stdio.h>

int add(int a, int b) {
    return a + b;
}

int subtract(int a, int b) {
    return a - b;
}

int(*get_add_func())(int, int) {
    return add;
}

int(*get_func_by_choice(int choice))(int, int) {
    if (choice == 1) {
        return subtract;
    }
    return add;
}

int main() {
    int(*func_ptr)(int, int);

    func_ptr = get_add_func();
    printf("%d\n", func_ptr(2, 1));

    func_ptr = get_func_by_choice(1);
    printf("%d\n", func_ptr(2, 1));

    return 0;
}

2. Implementing a Singly Linked List in C

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

typedef struct Node {
    int data;
    struct Node* next;
} Node, *LinkedList;

// Initialize a node
void init_node(LinkedList* head) {
    *head = (Node*)malloc(sizeof(Node));
    (*head)->next = NULL;
}

// Insert at the beginning
void insert_front(LinkedList* head) {
    Node* new_node;
    int value, count;
    printf("Enter number of elements to insert: ");
    scanf("%d", &count);
    printf("Enter values:\n");

    for (int i = 0; i < count; i++) {
        new_node = (Node*)malloc(sizeof(Node));
        scanf("%d", &value);
        new_node->data = value;
        new_node->next = (*head)->next;
        (*head)->next = new_node;
    }
}

// Insert at the end
void insert_back(LinkedList* head) {
    Node* new_node, *tail;
    int value, count;
    tail = *head;
    printf("Enter number of elements to insert: ");
    scanf("%d", &count);
    printf("Enter values:\n");

    for (int i = 0; i < count; i++) {
        new_node = (Node*)malloc(sizeof(Node));
        scanf("%d", &value);
        new_node->data = value;
        tail->next = new_node;
        tail = new_node;
    }
    tail->next = NULL;
}

// Display list
void display_list(LinkedList head) {
    Node* current = head->next;
    printf("List contents:\n");
    while (current != NULL) {
        printf("%d ", current->data);
        current = current->next;
    }
    printf("\n");
}

// Delete a node by position
void delete_node(LinkedList* head) {
    int pos, index = 0;
    printf("Enter position to delete: ");
    scanf("%d", &pos);

    Node* current = *head;
    while (current != NULL && index < pos - 1) {
        current = current->next;
        index++;
    }

    if (current == NULL || current->next == NULL) {
        printf("Invalid position.\n");
        return;
    }

    Node* temp = current->next;
    current->next = temp->next;
    free(temp);
}

3. Definition and Usage Example of Delegates in C#

In C#, a delegate is a reference type that holds a reference to a method. It's similar to pointers in C/C++, but more type-safe.

using System;

public delegate void GreetingDelegate();

class Program {
    static void Main() {
        GreetingDelegate greeting = new GreetingDelegate(SayHello);
        greeting += SayWorld;
        greeting();

        Console.WriteLine("--------");
        greeting -= SayWorld;
        greeting();
    }

    static void SayHello() => Console.WriteLine("Hello");
    static void SayWorld() => Console.WriteLine("World");
}

4. Functional Definitions and Examples of Action, Func, and Predicate

Action

Represents a method with no parameters and no return value.

using System;

void Greet() {
    Console.WriteLine("Greetings!");
}

Action greetAction = Greet;
greetAction();

Func

Represents a method that takes no parameters and returns a value of type T.

using System;

int GetNumber() {
    return 42;
}

Func<int> numberFunc = GetNumber;
Console.WriteLine(numberFunc());

Predicate

Represents a method that accepts one paramter and returns a boolean.

using System;

bool IsGreaterThanZero(int num) {
    return num > 0;
}

Predicate<int> predicate = IsGreaterThanZero;
Console.WriteLine(predicate(5)); // True

5. Reflection: Can Func Fully Replace Predicate?

No, Func cannot fully replace Predicate. Predicate<T> is a specialized version of Func<T, bool> designed specifically for filetring operations, offering better semantics and clarity in use cases involving conditions or tests.