สอบถามเรื่องการหาค่า Minimum ของ link list c++ ครับ

#include <iostream>

//Defind structure
typedef struct list {
    int info;
    struct list* link;
} node;
node *head, *null, *current, *temp, *pred;

int ShowMenu();
void INSERT_FN();
int _FindMax();
int Affter(int y);

void DisplaySingly(); //--
void CreateSingly(int Number); //--
void InsertFronSingly(int x); //--
void insertRearSingly(int y); //--
void insertMiddleSingly(int _info, int _Affter); //--
void DeleteSingly(int D);

void average();
void _Sum();

void max();
void min();

int main()
{
    int Menu;

    do {
        int A;
        int D;
		
		switch(Menu = ShowMenu())
		{
			case 1: INSERT_FN(); break;
			
			case 2: std::cout << "Delete:"; std::cin >> A; DeleteSingly(A); break;
			
			case 3: DisplaySingly(); break;
			
			case 4: _Sum(); break;
			
			case 5: average(); break;
			
			case 6: max(); break;
			
			case 7: min(); break;
		}
    } while (Menu != 8);

	std::cout << "\nExit\n";
	
    return 0;
}

int ShowMenu()
{
    int _Menu;

    std::cout << "\nPlease select menu\n";
    std::cout << " Insert  --> 1\n";
    std::cout << " Delete  --> 2\n";
    std::cout << " Display --> 3\n";
    std::cout << " Sum     --> 4\n";
    std::cout << " Average --> 5\n";
    std::cout << " Maximum --> 6\n";
    std::cout << " Minimum --> 7\n";
    std::cout << " Exit    --> 8\n";

    std::cout << "Select : ";
    std::cin >> _Menu;

    return _Menu;
}

void DisplaySingly(void)
{
    if (head == NULL)
        std::cout << "Empty List\n";

    else {
        current = head;
        while (current != NULL) {
            std::cout << current->info << std::endl;
            current = current->link;
        }
    }
}

//InsertFunction

void INSERT_FN()
{
    int Y;

    std::cout << "Insert : ";
    std::cin >> Y;

    if (head == null) {
        CreateSingly(Y);
    } else if (Y <= head->info) {
        InsertFronSingly(Y);
    } else if (Y >= _FindMax()) {
        insertRearSingly(Y);
    } else {
        insertMiddleSingly(Y, Affter(Y));
    }
}

void CreateSingly(int Number)
{
    if (head == NULL) {
        head = new node;
        head->info = Number;
        head->link = NULL;
    }
}

void InsertFronSingly(int x)
{
    if (head == NULL)
        std::cout << "Empty List";
    else {
        temp = new list;
        temp->info = x;
        temp->link = head;
        head = temp;
    }
}

int _FindMax(void)
{
    current = head;
    while (current->link != null) {
        current = current->link;
    }

    return current->info;
}

void insertRearSingly(int y)
{
    if (head == NULL)
        std::cout << "EMPTY LIST";
    else {
        temp = new node;
        temp->info = y;
        current = head;
        while (current->link != NULL)
            current = current->link;
        temp->link = NULL;
        current->link = temp;
    }
}

void insertMiddleSingly(int _info, int _Affter)
{
    if (head == NULL)
        std::cout << "Empty List";
    else {
        temp = new node;
        temp->info = _info;
        current = head;
        while (current->info != _Affter && current->link != NULL)
            current = current->link;
        temp->link = current->link;
        current->link = temp;
    }
}

int Affter(int y)
{
    current = head;

    while ((y < current->info) or (y > current->link->info)) {
        current = current->link;
    }

    return current->info;
}

void DeleteSingly(int D)
{
    int DELETE;

    if (head->info == D) {
        current = head;
        head = head->link;
        DELETE;
        current;
    } else {
        pred = head;
        current = head->link;
        while (current->link != NULL && current->info != D) {
            pred = current;
            current = current->link;
        }
        if (current->info = D) {
            pred->link = current->link;
            DELETE;
            current;
        } else
            std::cout << "NOT FOUND";
    }
}

void _Sum()
{
    int sum = 0;
    current = head;
    while (current != NULL) {
        sum = sum + current->info;
        current = current->link;
    }
    std::cout << "Sum=" << sum << std::endl;
}

void average()
{
    float sum = 0;
    int counter = 0;
    current = head;
    while (current != NULL) {
        sum = sum + current->info;
        counter++;
        current = current->link;
    }
    std::cout << "average=" << sum / counter << std::endl;
}

void max()
{

    int max = 0;
    current = head;
    for (current = head->link, max = head->info; current; current = current->link)
        if (current->info > max)
            max = current->info;

    std::cout << "Maximum=" << max << std::endl;
}

void min()
{
    int min;
    for (current = head->link, min = head->info; current; current = current->link)
        if (current->info < min)
            min = current->info;

    std::cout << "Minimum=" << min << std::endl;
}