Tak, tady je ten finální kód

#include <iostream>
#include <cstdlib>
#include <ctime>

using namespace std;

const int N = 3; //pocet pokladen
const int M = 2; //pocet zakazniku
const int P = 3; //max. pocet polozek v nakupu

struct cus{ //zakaznik
	int id;
	int items;
	cus *next;
};

struct queue{ //fronta
	cus *head, *tail;
	int size;
};

bool isEmpty(queue arr[]){ //kontrola pole, jestli je prazdne
	int sum = 0; //pocet prazdnych front
	for(int i = 0; i < N; ++i){
		if(arr[i].size == 0){
			sum++;
		}
	}
	if(sum == N){
		return true;
	}
	return false;
}

void init(queue arr[]){ //inicializace pole na zacatku

	for(int i = 0; i < N; ++i){
		arr[i].head = arr[i].tail = NULL;
		arr[i].size = 0;
	}

}

int main(){
	queue *arr = new queue[N];
	init(arr);

	int total = 1; //poradi zakazniku

	srand(time(NULL)); //pro urceni nahodneho cisla nakupu

	do{

		//generovani noveho zakaznika
		if(total <= M){
			cus *newC = new cus; //novy zakaznik
			newC->id = total;
			newC->items = rand() % P + 1;

			cout << "G" << newC->id << "[" << newC->items << "]" << " ";

			++total;


			//urceni nejkratsi fronty a zarazeni zakaznika
			int qMin = 0; //index nejkratsi fronty
			int lMin = arr[0].size; //delka nejkratsi fronty
			for(int i = 0; i < N; ++i){
				if(lMin > arr[i].size){
					lMin = arr[i].size;
					qMin = i;
				}
			}

			//zarazeni zakaznika na konec nejkratsi fronty
			if(arr[qMin].head == NULL){
				arr[qMin].head = newC;
				arr[qMin].head->next = NULL;
			}else if(arr[qMin].tail == NULL){
				arr[qMin].head->next = newC;
				arr[qMin].tail = newC;
				arr[qMin].tail->next = NULL;
			}else{
				arr[qMin].tail->next = newC;
				arr[qMin].tail = newC;
				arr[qMin].tail->next = NULL;
			}

			arr[qMin].size++; //zvetsim velikost pole +1

			cout << "V" << newC->id << "[F" << qMin << "]" << " ";
		}

		//"odbaveni" zakaznika na pokladne
		for(int i = 0; i < N; ++i){ //prochazim pokladny a hledam, jestli je na headu hodnota - zakaznik
			if (arr != NULL && arr[i].head != NULL) {
				if (arr[i].head->items == 0){

					cout << "O" << arr[i].head->id << "[" << arr[i].size -1 << "] ";

					arr[i].head = arr[i].head->next;
					if(arr[i].head == arr[i].tail){
					    arr[i].tail = NULL;
					}

					arr[i].size--;
				}else{
					arr[i].head->items--;
					cout << "K" << arr[i].head->id << "[" << arr[i].head->items << "] ";
				}
			}
		}
	}while(isEmpty(arr) == false);

	cout << endl;
	delete []arr;
	return 0;
}