main.c

// Programmed and commented(for better-explanation) by Ajay Kumar Mishra :)
#include <stdio.h>
#include <stdlib.h>
#include <math.h>
#include <time.h>
#include <string.h>
#include "queue.h" // contains the Customer and Queue defs
#include "stats.h" // contains the statistical formulae functions


int poisson(double lam){ // Knuth's algo for random variate generation(Poisson)  
  double L = exp(-lam);
  double p = 1.0;
  int k = 0;

  do{
    k++;
    double u = rand()/(RAND_MAX + 1.0);
    p *= u;
  } while(p > L);
  return k - 1;
}


int main(){
  srand(time(NULL)); // seeding on the basis of current time
  
  double lambda;  // lambda(or mean value) as required in the formula of Poisson PMF
  printf("Enter avg no. of customers per minutee(ie lambda): "); scanf("%lf", &lambda);
  int nextID = 1, tellerBusyTime = 0;  // initially, teller's not busy
  
  Queue q; initQueue(&q);
  int capacity = 10000; // let us initiate waiting time list as 10^4 for now
  double *waitTimes = (double *) malloc(sizeof(double) * capacity); // malloc instead of calloc, more efficient and calloc is not really needed now
  int servedCnt = 0; // a no-brainer, initially the teller didn't serve

  for(int i = 0; i < (8 * 60); ++i){ // 8 hours * 60 = 480 minutes, ie 480 iterations
    int noOfarrivals = poisson(lambda);
    for(int j = 0; j < noOfarrivals; ++j){
      enqueue(&q, nextID++, i);
    }      
    if(tellerBusyTime > 0){
      --tellerBusyTime; // decrease 1 minute(per iteration) is the teller is busy
    } else if(q.head != NULL){ // if teller is not busy and there's still someone left in the waiting queue
      Customer *c = dequeue(&q);
      double w8time = i - c->arrivalTime;
      if(servedCnt >= capacity){
        capacity *= 2;
        waitTimes = realloc(waitTimes, sizeof(double) * capacity); // reallocating if the pre-defined size limit is exceeded
      }
      waitTimes[servedCnt++] = w8time; 
      tellerBusyTime = 2 + rand()%2;
      free(c);
    }   
  }

  if(servedCnt == 0) { // served count is 0, ie no customers served 
    printf("No customers were served\n");
    return 0;
  }
  // now just applying the functions to get the desired stat-results(I made that up lmao) -> 
  double avg = mean(waitTimes, servedCnt);
  double med = median(waitTimes, servedCnt);
  double mod = mode(waitTimes, servedCnt);
  double sd = stdDev(waitTimes, servedCnt, avg);
  double max = waitTimes[0];
  for(int i = 0; i < servedCnt; ++i){
    if(waitTimes[i] > max){
      max = waitTimes[i];
    }        
  }   

  printf("\n===== BANK QUEUE SIMULATION REPORT WITH POISSON DISTRIBUTION =====\n");
  printf("Total customers served: %d\n", servedCnt);
  printf("Average wait time: %.2f minutes\n", avg);
  printf("Median wait time: %.2f minutes\n", med);
  printf("Mode wait time: %.2f minutes\n", mod);
  printf("Standard deviation: %.2f\n", sd);
  printf("Longest wait time: %.2f minutes\n", max);
  printf("\n===== THANK YOU FOR USING MY SILLY PROGRAM, GET ME A CupOfCoffee ALREADY :) =====\n"); // is my program really THAT silly? 
   
  free(waitTimes);
  return 0; 
}