Csci 4651 Problem set 4

Problem 1: Algol 60 Pass-by-Name (5 pts)

Exercise 5.2 pp. 122-123.

Problem 2: pointers and functions in C++ (10 pts)

To run a C++ program:

Question 1

Write a void C++ function order that takes two pointers to int, checks if the value at the first address is larger than at the second one, and if it is, switches the values at the two addresses. I.e. if I have n = 7, m = 2 then after the call order(&n,&m) n should have the value 2, and m the value 7.

Submit the file with your function and the testing code. Your program must compile and run on the dungeon machines. Important: Even if you are familiar with a different C++ style of declaring parameter passing by reference, please use the style that was used in the example in class.

Question 2

Consider the following two C++ loops, where n and m are integer (int) variables and p and q are pointers to ints.


  while(n >= m) {
    n = n - 1;
  }

  while (*p >= *q) {
    *p = *p - 1;
  }

For each of the loop please answer: is it guaranteed to terminate? If yes, please explain why. If not, please write a program that initializes variables used in the loop in such a way that the program goes into an infinite loop (Ctrl-C stops a program).

Extra credit (added 2/23): are there additional possiblities of divergence if the type of the variables is not restricted to ints?


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