4. (10 pts) Explain what the following Scheme code is doing (define (make-stream

Question

4. (10 pts) Explain what the following Scheme code is doing (define (make-stream n f) (define (next m) (next n)) (define head car) (define (tail stream) ((cdr stream))) (define (nth stream n) (if (- n 0) (head stream) (nth (tail stream) ( n 1)))) (define even (make-stream 0 (lambda (n) (+ n 2)))) Try it out in Scheme48 and check the values of the following expressions: even (head even) (head (tail even)) (head (tail (tail even)) (head (tail (tail (tail even)) )) (nth even 5) (nth even 1000) Explain what the lambda in make-stream is good for, where this function is called, and how tail and nth work. To see what's going on, trace manually through the execution of (head (tail (tail even))

Explanation / Answer

#include
using namespace std;

int main(void)
{
// structure:
// while ( condition )
//  statement;
// do
//  statement;
// while ( condidion );

// 1 counted loop
// 1.1 input count
int lowRange;
int highRange;
while (true)
{
  cout << "Enter a Numerical Range with a low and high bound: ";
  cin >> lowRange>> highRange;
  cin.ignore(999, ' ');
  if (cin.fail())
  {
   cin.clear();
   cin.ignore(999, ' ');
   cout << "data format error, try again" << endl;
   continue;
  }
  if ( lowRange >= 0)
   break; // end test
  cout << "no negative numbers, try again" << endl;
}

// 1.2
int howManyTimesAccomplished = 0;
while (howManyTimesAccomplished < lowRange)
{
  // 1.2.1 output greeting
  cout << "Hello, World!" << endl;
  // howManyTimesAccomplished = howManyTimesAccomplished + 1;
  // howManyTimesAccomplished += 1;
  ++howManyTimesAccomplished; // howManyTimesAccomplished++
}

// 1.3 output greetings
for (int sumRange = 0
  ; int sumTwoRange = 1
  ; sumTwoRange <= highRange
  ;)
  cout << "Hello, World!" << endl;

cout << endl;

// 2 more greetings (not counted):
cout << "more greetings" << endl;
while (true)
{
  // 2.1 output greeting
  cout << "Hello World" << endl;

  // 2.2 ask if user wants to do again
  bool doAgain;
  while (true)
  {
   char userResponse;
   cout << "Do you want to do it again? ";
   cin >> userResponse;
   cin.ignore(999, ' ');
   if (cin.fail())
   {
    cin.clear();
    cin.ignore(999, ' ');
    cout << "Please enter y or n." << endl;
    continue;
   }
   if (userResponse == 'y' || userResponse == 'Y')
   {
    doAgain = true;
    break;
   }
   if (userResponse == 'n' || userResponse == 'N')
   {
    doAgain = false;
    break;
   }
   cout << "Please enter y or n." << endl;
  }
  if (!doAgain) break;
}

}

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