teaching machines

CS 330 Lecture 23 – Cisms Cont’d

April 1, 2015 by Chris Johnson. Filed under cs330, lectures, spring 2015.

Agenda

• what ?s
• enums and type safety
• the C preprocessor
• macro danger
• dynamic memory allocation
• memory allocation

When do I dynamically allocate memory?

1. When you don’t know how much memory you’ll need at compile time. You don’t know if the size depends on a function parameter.
2. When you allocate memory within a function but need the memory to outlive the function.

Otherwise, use the stack.

When do I need pointers?

1. When you need cheap sharing of data from caller to callee.
2. When you need a function to return multiple values (out parameters).
3. When you dynamically allocate.

Code

blackjack.c

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

enum suit_t {
  DIAMONDS,
  HEARTS,
  CLUBS,
  SPADES
};

enum rank_t {
  ACE = 1,
  DEUCE,
  THREE,
  FOUR,
  FIVE,
  SIX,
  SEVEN,
  EIGHT,
  NINE,
  TEN,
  JACK = 10,
  QUEEN = 10,
  KING = 10
};

struct card_t {
  enum suit_t suit;
  enum rank_t rank;
};

int score(struct card_t *hand, int ncards) {
  int sum = 0;
  int naces = 0;

  for (int i = 0; i < ncards; ++i) {
    if (hand[i].rank == ACE) {
      ++naces;
    } else {
      sum += hand[i].rank;
    }
  }

  if (naces > 0) {
    if (sum + 11 + naces - 1 <= 21) {
      sum += 11 + naces - 1;
    } else {
      sum += naces;
    }
  }

  return sum;
}

int main(int argc, char **argv) {
  struct card_t hand[] = {
    {CLUBS, JACK},
    {SPADES, ACE},
    {101, -5}
  };

  printf("score(hand): %d\n", score(hand, 3));

  return 0;
}

include.c

#include "limits.h"

int main(int argc, char **argv) {
  
  return 0;
}

c2i.c

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

/* #define C2I(c, r, width) c + r * width */
#define C2I(c, r, width) (c) + (r) * (width)

int main(int argc, char **argv) {
  printf("C2I(3, 1, 4): %d\n", C2I(3, 1, 4));
  printf("C2I(3, 1, 4): %d\n", C2I(3, 1 + 1, 4));
  return 0;
}

BlackJack21.java

public class BlackJack21 {

  public static void main(String[] args) {
    new Card(Suit.SPADES, Rank.NINE);
//    new Card(101, -5);
  }
}

class Card {
  private Suit suit;
  private Rank rank;
  
  public Card(Suit suit, Rank rank) {
    this.suit = suit;
    this.rank = rank;
  }
}

enum Suit {
  HEARTS,
  DIAMONDS,
  CLUBS,
  SPADES
}

interface Foo {
  enum Force {
    GOOD,
    EVIL,
  };
}

enum Rank {
  ACE(1),
  DEUCE(2),
  THREE(3),
  FOUR(4),
  FIVE(5),
  SIX(6),
  SEVEN(7),
  EIGHT(8),
  NINE(9),
  TEN(10),
  JACK(10), 
  QUEEN(10), 
  KING(10);
  
  private int value;
  
  private Rank(int value) {
    this.value = value;
  }
}

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