Chapter 18 // Exercise 11 - Principles & Practice Using C++

In this exercise I am using Visual Studio 2017 and the std_lib_facilities header provided by Stroustrup.

Chapter 18 // Exercise 11

Look up (e.g., on the web) skip list and implement that kind of list. This is not an easy exercise.

Github: https://github.com/l-paz91/principles-practice/tree/master/Chapter%2018/Exercise%2011

I sighed...I sighed when I googled "skip list". Why Bjarne? This exercise took me a good 2 weeks as I was determined to solve it using only pointers and arrays. You can use a vector to make it a bit simpler but I noticed that the vector implementation I did bumped the memory usage of the program way up; I was a little shocked at the overhead vector brings.

To solve this I used a paper written by William Pugh (the inventor of Skip lists) found here:

https://www.epaperpress.com/sortsearch/download/skiplist.pdf

It contains pseudo code for each function but it's written in Pascal. I had fun trying to decode that....not. Pascal for the most part is relatively similar to C++; the main issue was working out when I had to de-reference or new something up. At one point I was convinced his code didn't work but of course it was just me that wasn't working.

One of the most annoying parts of this task though was trying to debug it. As all my arrays had to be dynamically allocated at runtime, that meant I could only access them via pointers. Pointers only point at the first value of the array so the watch window isn't that helpful. That is unless you know the tricks of the watch window!

A skip list is pretty much made up of Nodes, a node contains a value and an array of pointers to other nodes ahead of it. mHead is the start of the Skip list and we can see here that it's array mNext is only showing us mNext[0]. How do you find out what mNext[1] is at this point?

Well, just right click on the value in Local values, add a watch to it (the right click menu didn't show up in the recording), then add the subscript operators on the end and access whichever part of the array you want!

That's great for specific parts of the array. But what if you want to glance quickly at the entire array? Well if the array has been dynamically allocated, in the watch window, click on a new line and type in:

nameOfPointer, numberOfElements

hit enter and Visual Studio will give you a normal looking array list!

(All those values are supposed to be null by the way).

Now, this only works with ints (I'm not doing templated types just yet although I can see Bjarne making that an exercise in later chapters). And I'm sure there is an error somewhere but for the most part it "works on my machine" lol. I've already spent a bit too much time on this one exercise.

Chapter 18 // Exercise 10 - Principles & Practice Using C++

In this exercise I am using Visual Studio 2017 and the std_lib_facilities header provided by Stroustrup.

Chapter 18 // Exercise 10

Look at the "array solution" to the palindrome problem in section 18.7.2. Fix it to deal with long strings by (a) reporting if an input string was too long and (b) allowing an arbitrarily long string. Comment on the complexity of the two versions.

Github: https://github.com/l-paz91/principles-practice/blob/master/Chapter%2018/Exercise%2010

In this one, he didn't say we couldn't use the std library, so I used cin.getline() instead of just the normal cin >>. This allows whitespace to be read as getline() only skips new lines (unless you give it a different delimiting character). Getline() will then continue reading up until the max and append a terminating 0, regardless of whether there were any characters to read.

The next problem was checking if the reading stopped because the buffer ran out of characters or there were too many characters. We can use cin.fail() to check if the stream failed to read. The failbit will be set if it reaches the end of the buffer and still hasn't encountered the delimiting character. A message can then be printed and cin needs to be reset for the next iteration.

I'm not sure if we were supposed to do it a different way as this wasn't entirely complex so I can't comment on the complexity of the two versions. 

http://www.cplusplus.com/reference/istream/istream/getline/

Chapter 18 // Exercise 9 - Principles & Practice Using C++

In this exercise I am using Visual Studio 2017 and the std_lib_facilities header provided by Stroustrup.

Chapter 18 // Exercise 9

Consider the memory layout in section 17.4. Write a program that tells the order in which static storage, the stack, and the free store are laid out in memory. In which direction does the stack grow: upward toward higher addresses or downward toward lower addresses? In an array on the free store, are elements with higher indices allocated at higher or lower addresses?

Github: https://github.com/l-paz91/principles-practice/blob/master/Chapter%2018/Exercise%209

So going off Bjarne's description of static, stack and heap I managed to print some global variables and a bunch of locals/new'd values but I'm unsure what to do with the stack? His description says "...It sets aside some memory to be used when you call functions, and they need space for their arguments and local variables". You can print the address of where the function is but I don't think you can print the size of the function? I had a look around and that generally is something that can't be done.

I also couldn't compare the addresses for different functions unless they're identical but the ones included in the program were in places near each other but didn't trend one specific way.

const char*'s and newed up char arrays always grew downwards but newed up double arrays grew upwards.

I'm not convinced I've done this exercise correctly.

Chapter 18 // Exercise 8 - Principles & Practice Using C++

 In this exercise I am using Visual Studio 2017 and the std_lib_facilities header provided by Stroustrup.

Chapter 18 // Exercise 8

Rewrite all the functions in section 18.7 to use the approach of making a backward copy of the string and then comparing; for example, take "home", generate "emoh", and compare those two strings to see that they are different, so home isn't a palindrome.

Github: https://github.com/l-paz91/principles-practice/blob/master/Chapter%2018/Exercise%208

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Chapter 18 // Exercise 7 - Principles & Practice Using C++

In this exercise I am using Visual Studio 2017 and the std_lib_facilities header provided by Stroustrup.

Chapter 18 // Exercise 7

Write versions of the cat_dot()s from the previous exercises to take C-style strings as arguments and return a free-store-allocated C-style string as the result. Do not use standard library functions or types in the implementation. Test these functions with several strings. Be sure to free (using delete) all the memory you allocated from the free store (using new). Compare the effort involved in this exercise with the effort involved for exercises 5 and 6.

Github: https://github.com/l-paz91/principles-practice/blob/master/Chapter%2018/Exercise%207

Creating this cat_dot was fairly straightforward if a little cumbersome.