h06: Chapter 7 and 10: Pointers

Read Chapter 7.1 - 7.2 up to page 397. Also read this handout on Pointers and Memory: http://cslibrary.stanford.edu/102/PointersAndMemory.pdf You don’t need to turn this homework in. To earn credit for this homework, complete the corresponding quiz on gauchospace AFTER you have completed the pen and pencil version of the homework. The quiz will be available one day before the due date indicated on the homework.

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1.(5 pts) What is the output of the following code? If there’s an error that will not allow an output, point it out. Briefly justify your answer.

int arr[5];
for (int i = 0; i < 5; i++) {
  if (i < 3) arr[i] = 'a';
  else arr[i] = 'z';
  cout << arr[i] << endl;  }

2.(5 pts) What is the output of the following code? If there’s an error that will not allow an output, point it out.

int arr[7] = {5};
for (int i = 0; i < 7; i++)
  cout << arr[i] + i <<" ";

3.(5 pts) What is the output of the following code? If there’s an error that will not allow an output, point it out.

int codes[] = {44, 66, 83, 973, -977};
for (int count : codes) {
  if ( (count/2) < 50 )
    cout << count << endl;
  else cout << "invalid" << endl; }

4.(5 pts) Draw a diagram to show how the content of the array ‘nums’ changes in memory after every line of the following code is executed. Start by showing the elements of the array in memory when the array is initialized. Every time the element of an array changes, you may indicate the change by crossing out the old value and writing in the new value.

int nums[] = {44, 66, 83};
int tmp = nums[0];
nums[0] = nums[1];
nums[1] = nums[2];
nums[2]= tmp;

5.(5 pts) Describe in your own words what the code in the previous question does. Your description of the code should be as abstract as possible. For example..”the above code sorts the elements of the array in ascending order…”

6.(10 pts) Write the definition of a function named ‘reverse’ that takes two parameters: an integer array and the number of elements of the array. The function should reverse the order of elements of the array. The function should not return anything. See below for an example of expected outcome when the reverse function is called:

int nums[] = {10,20,30,40,50};
reverse(nums, 5);// The order of elements should be reversed after this
for(int i=0;i<5;i++)
   cout<< nums[i]<<" "

The output of the above code should be: 50 40 30 20 10

7.(4 pts) List two reasons why you might choose to pass parameters to a function by address or reference, rather than by value in your C++ programs.

8.(6 pts) Draw a pointer diagram to demonstrate how the state of memory changes as the following code is executed. Cross out old values/arrows and draw new ones. Is this program likely to result in a segmentation fault? If so, why?

   int num = 10, *ptr1 = &num, *ptr2=0;
   if (ptr2) ptr1 = ptr2;
   else if(ptr1) ptr2 = ptr1;
   (*ptr1)++;

9.(8 pts) On page 14 of the “Pointers and Memory” handout there is a reference to the “Amperand (&)” Bug in the TAB() function. Draw a trace of the local variables of the functions Victim() and TAB() on the run-time stack as these functions are executed. Your diagram should be similar to the one provided on page 13. Your diagram should depict exactly three instances in program execution - T1: Right after the first statement of Victim(), T2: right before the return statement in TAB(), T3: Right after the call to TAB(). Use your diagram to explain the “Amperand (&)” bug and why it is likely to lead to a runtime error when the last line of the Victim() is executed?