22 November

Some examples of reference parameters

void swap(int& a, int& b)
{
   int t = a;
   a = b;
   b = t;
}

void func(int a, int& b)
{
   b = a+2;
   a = a+1;
}

int main()
{
   int x = 5, y = 3;
   swap(x,y);
   printf("%d,%d\n", x, y);
   func(8,x); // okay
   //func(x,8); // error.
   return 0;
}

A quiz-like sample program

int grok(int& x, int y, int& z)
{
  x = x + y;
  y = x + z;
  z = x + y;
  return x+y+z;
}

int main()
{
  int y = 2, z = 3, w = 4;
  int b = grok(y,z,w);
  printf("%d,%d,%d,%d\n", y,z,w,b);
  return 0;
}

Using a reference parameter for Blackjack

void deal_one_card(int& rank, int& suit)
{
  rank = rand()%13+1;
  suit = rand()%4;
}

int main()
{
  srand(time(NULL));
  int rank=0, suit=0;
  deal_one_card(rank, suit);
  printf("%d of %d\n", rank, suit);
}

Arrays: numeric computation

const int SIZE = 100;
int main()
{
  int a[SIZE]; // allocate SIZE slots for array

  // initialize array to squares of indexes
  for(int i = 0; i < SIZE; i++)
  {
    a[i] = i*i;
  }

  // sum of squares
  for(int i = 1; i < SIZE; i++)
  {
    a[i] = a[i] + a[i-1];
  }

  // print array index and values
  for(int i = 0; i < SIZE; i++)
  {
    printf("%d -> %d\n", i, a[i]);
  }
  return 0;
}

Arrays: tally how many rolls on 2 simulated dice

const int ROLLS = 1000;
const int DICE_SIDES = 6;
const int MAX_OF_2_DICE = DICE_SIDES*2;
int main()
{
  srand(time(NULL));
  int frequencies[MAX_OF_2_DICE+1];
  // initialize array to all zeroes
  for(int i = 0; i <= MAX_OF_2_DICE; i++)
  {
    frequencies[i] = 0;
  }
  // simulate rolling dice a lot
  for(int i = 0; i < ROLLS; i++)
  {
    int roll1 = rand()%6+1;
    int roll2 = rand()%6+1;
    frequencies[roll1+roll2]++;
  }
  // print array
  for(int i = 1; i <= MAX_OF_2_DICE; i++)
  {
    printf("%d -> %d\n", i, frequencies[i]);
  }
  return 0;
}