Week 1 Homework of C++ for C Programmers

rolling_two_dice.c

#include <stdlib.h>   // For generating random value:
                      // rand()
#include <stdio.h>    // For basic input and output:
                      // printf
                      // scanf
#include <time.h>     // For getting the time in seconds since the Epoch
                      // time()

// Label the sides of the dice.
#define SIDES 6
// Number of the dice that will be rolled.
#define NUM_OF_DICE 2

// The minimal result of rolled dice is NUM_OF_DICE * 1.
#define MIN_RESULT NUM_OF_DICE
// The maximal result of rolled dice is NUM_OF_DICE * SIDES.
#define MAX_RESULT (NUM_OF_DICE * SIDES)

// Returns a pseudo-random integer between 1 and 6.
#define RAND_SIDE (rand() % SIDES + 1)

// Returns the index for our outcomes of the rolling dice.
#define GET_INDEX(result) (result - MIN_RESULT)

int main() {
  // Use time(NULL) as seed by the pseudo-random number generator algorithm.
  srand(time(NULL));

  // A prompt for user to enter the trials.
  printf("\nEnter number of trials: ");

  // The times that dice will be rolled.
  int trials = 0;
  // Read the value from standard input and assigned it to trials.
  scanf("%d", &trials);

  // The results of the total of the rolled dice.
  // We will have (MAX_RESULT - MIN_RESULT + 1) results.
  // The outcomes[(R1 + R2 + ...) - MIN_RESULT] will record the times of
  // the results that are equal to (R1 + R2 + ...),
  // where R1 is the result for rolling dice 1,
  // R2 is the result for rolling dice 2, ... and so on.
  int outcomes[MAX_RESULT - MIN_RESULT + 1] = { 0 }; // Initialized to 0.
  int times = 0;
  for (times = 0 ; times < trials ; times++) {
    int dice = 0, total = 0;
    for (dice = 0 ; dice < NUM_OF_DICE ; dice++) {
      total += RAND_SIDE;
    }
    outcomes[GET_INDEX(total)]++;
  }

  // Shows the results:
  int result = 0;
  for (result = MIN_RESULT ; result <= MAX_RESULT ; result++) {
    double probability = (double)outcomes[GET_INDEX(result)] / trials;
    printf("result: %d, times: %d, probability: %lf\n",
           result, outcomes[GET_INDEX(result)], probability);
  }

  return 0;
}

rolling_two_dice.cpp

#include <iostream>   // For basic input and output:
                      // std::cin
                      //      cout
                      //      endl
#include <random>     // For random number generation facilities:
                      // std::random_device
                      //      default_random_engine
                      //      uniform_int_distribution

// The NAME.h here becomes cNAME.h. For example, time.h becomes ctime.
// The prefix "c" means import what would also be a library in C.
// Notice that the .h header files are still available here.

// The Usage of macro:
// The text defined in macros will be substituted by preprocessor.
// The macro functions runs faster than the normal function call
// because it won't need to jump in the memory stack.
// However, it may be difficult to debug
// when there is someting wrong in macro.
// It creates more opportunity for errors than equivalent implementation
// in language that can be checked by language rules.

// Label the sides of the dice.
const int SIDES = 6;
// Number of the dice that will be rolled.
const int NUM_OF_DICE = 2;

// The minimal result of rolled dice is NUM_OF_DICE * 1.
const int MIN_RESULT = NUM_OF_DICE;
// The maximal result of rolled dice is NUM_OF_DICE * SIDES.
const int MAX_RESULT = NUM_OF_DICE * SIDES;

// Returns the index for our outcomes of the rolling dice.
inline int GET_INDEX(int result) {
  return result - MIN_RESULT;
}

// using namespace std for input/output
using std::cin;
using std::cout;
using std::endl;

// using namespace std for random number generation facilities
using std::random_device;
using std::default_random_engine;
using std::uniform_int_distribution;

int main() {
  // Seed with a real random value
  // for the pseudo-random number generator algorithm.
  random_device randDev;
  default_random_engine randEng(randDev());

  // Produce random integer values,
  // uniformly distributed on the closed interval [1, 6]
  uniform_int_distribution<int> uniDist(1,6);

  // A prompt for user to enter the trials.
  cout << "\nEnter number of trials: ";

  // The times that dice will be rolled.
  int trials = 0;
  // Read the value from standard input and assigned it to trials.
  cin >> trials;

  // The results of the total of the rolled dice.
  // We will have (MAX_RESULT - MIN_RESULT + 1) results.
  // The outcomes[(R1 + R2 + ...) - MIN_RESULT] will record the times of
  // the results that are equal to (R1 + R2 + ...),
  // where R1 is the result for rolling dice 1,
  // R2 is the result for rolling dice 2, ... and so on.
  int outcomes[MAX_RESULT - MIN_RESULT + 1] = { 0 }; // Initialized to 0.

  for (int times = 0 ; times < trials ; times++) {
    int total = 0;
    for (int dice = 0 ; dice < NUM_OF_DICE ; dice++) {
      total += uniDist(randEng);
    }
    outcomes[GET_INDEX(total)]++;
  }

  // Shows the results:
  for (int result = MIN_RESULT ; result <= MAX_RESULT ; result++) {
    double probability = (double)outcomes[GET_INDEX(result)] / trials;
    cout << "result: " << result <<
            ", times: " << outcomes[GET_INDEX(result)] <<
            ", probability: " << probability << endl;
  }

  return 0;
}

sum.c

#include <stdio.h>
#define N 40

void sum(int* accum, int num, int data[]) {
  // Set the value pointed by accum to zero first, in case it already has value.
  *accum = 0;
  int i = 0;
  for (i = 0; i < num ; i++) {
    *accum += data[i];
  }
}

int main() {
  // Declare and initialize data array.
  int data[N] = { 0 };
  int i = 0;
  for (i = 0 ; i < N ; i++) {
    data[i] = i;
  }

  int accum = 0;
  sum(&accum, N, data);

  printf("Sum is %d\n", accum);

  return 0;
}

sum.cpp

#include <iostream>

// Use const to replace #define N 40
const int N = 40;

// Use '&' reference to replace pointer.
void sum(int& accum, int num, int data[]) {
  // Set the accum to zero first, in case it already has value.
  accum = 0;
  // Declare local variable i in the for-loop scope.
  for (int i = 0; i < num ; i++) {
    accum += data[i];
  }
}

int main() {
  // Declare and initialize data array.
  int data[N] = { 0 };
  for (int i = 0 ; i < N ; i++) {
    data[i] = i;
  }

  int accum = 0;
  // Pass accum as reference instead of pointer.
  sum(accum, N, data);

  std::cout << "Sum is " << accum << std::endl;

  return 0;
}