Chapter 17 // Exercise 14 - Principles & Practice Using C++

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

Chapter 17 // Exercise 14

Could the "list of gods" example from Section 17.10.1 have been written using a singly-linked list; that is,could we have left the prev member out of Link? Why might we want to do that? For what kind of examples would it make sense to use a singly-linked list? Re-implement that example using only a singly-linked list.

Github: https://github.com/l-paz91/principles-practice/tree/master/Chapter%2017/Exercise%2014

Eurgh why. Without prev it would be very hard to find the start of the list. The pointer can be changed to point at something else when an element is inserted/removed. We would need to store a pointer to the first value.

Insertion would be trickier as well as you would have to start from a, advance n times to the insertion point so you know the previous then assign the new successors. Just use a vector.

I tried googling best use cases for a Singly linked list and I couldn't really find any.

And with that, another chapter bites the dust. This was a good chapter though. I have so many notes on pointers and memory allocation. I'm also halfway through the book! Just 590 pages out of 1216.

Chapter 17 // Exercise 13 - Principles & Practice Using C++

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

Chapter 17 // Exercise 13

Modify the Link class from section 17.10.1 to hold a value of a struct God. struct God should have members of type string: name, mythology, vehicle, and weapon. For example, God{"Zeus", "Greek", "", "lightning"} and God{"Odin", "Norse", "Eight-legged flying horse called Sleipner", "Spear and Gungnir"}. Write a print_all() function that lists gods with their attributes one per line. Add a member function add_ordered() that places its new element in its correct lexicographical position. Using the Links with the values of type God, make a list of gods from three mythologies; then move the elements (gods) from that list to three lexicographically ordered lists - one for each mythology.

Github: https://github.com/l-paz91/principles-practice/tree/master/Chapter%2017/Exercise%2013

What in the ever-living christ? I really hated this exercise when I started it. In fact, I procrastinated so much in doing this exercise that I made a slenderman game in Unreal Engine and did the infamous Blender Donut tutorial:

Anyway, I finally did it and by the end of it, I have to admit, I understood linked lists WAY better than I did before. Don't skip the exercises everyone; they actually work.

Sure, this is not the greatest code ever written but I did it!

Chapter 17 // Exercise 11, 12 - Principles & Practice Using C++

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

Chapter 17 // Exercise 11, 12

11. Complete the "list of gods" example from section 17.10.1 and run it.

12. Why did we define two versions of find().

Github: https://github.com/l-paz91/principles-practice/tree/master/Chapter%2017/Exercise%2011

Wow, linked lists are confusing. I never want to read prev->succ = prev if !prev then succ = prev->succ etc....

For exercise 12 I had to go read the small section in Chapter 18. Basically, it's to stop someone from change what Link* is pointing at. In the functions I try to always assign the pointer to a new temp pointer to avoid messing with the original. I feel like this is the same case here.

Chapter 17 // 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 17 // Exercise 10

Look at your solution of exercise 7. Is there any way that input could get the array to overflow; that is, is there any way you could enter more characters than you allocated space for (a serious error)? Does anything reasonable happen if you try to enter more characters than you allocated?

Github: https://github.com/l-paz91/principles-practice/blob/master/Chapter%2017/Exercise%207%2C%208

Fortunately, the version of cin.get() that I used only gets up to the specified amount of characters. So I pass it the char pointer then specify 256 (as that is the size of the array) and give it a deliminating character. So it will either stop reading at '!'  or once it reads in 256 characters.

Chapter 17 // 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 17 // Exercise 9

Which way does the stack grow: up (toward higher addresses) or down ( towards lower addresses)? Which way does the free store initially grow (that is, before you use delete)? Write a program to determine the answers.

Github: https://github.com/l-paz91/principles-practice/blob/master/Chapter%2017/Exercise%209

If you're newing via a for loop it seems to pick addresses near to each other? Interestingly, it appears to grow downwards for numbers and upwards for chars. I don't think it's set in stone though as I've seen the free store ints going upwards.

Chapter 17 // Exercise 7, 8 - Principles & Practice Using C++

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

Chapter 17 // Exercise 7, 8

7. Write a program that reads characters from cin into an array that you allocate on the free store. Read individual characters until an exclamation mark (!) is entered. Do not use a std::string. Do not worry about memory exhaustion.

8. Do exercise 7 again, but this time read into a std::string rather than to memory you put on the free store (string knows how to use the free store for you).

Github: https://github.com/l-paz91/principles-practice/blob/master/Chapter%2017/Exercise%207,%208

There's no need to re-invent the wheel here as cin will do all the hardwork for you, all you need to do is supply it with a maximum stream buffer size. Back in chapter 7, we extensively used cin.get() during the creation of the calculator. cin.get() has quite a few different overloads which you can find here:

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

I used the c-string version istream& get(char* s,  streamsize n, char delim). This allows you to give cin a custom delimiting character (in our case !) and will read characters in and store them at the given address up to streamsize. Simples.

Technically it's cheating but he did say use cin.

As for 8, getline() also has a version that allows you to specify a delimiting character:

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

Chapter 17 // Exercise 6 - Principles & Practice Using C++

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

Chapter 17 // Exercise 6

This chapter does not say what happens when you run out of memory using new. That's called 'memory exhaustion'. Find out what happens. You have two obvious alternatives: look for documentation, or write a program with an infinite loop that allocates but never deallocates. Try both. Approximately how much memory did you manage to allocate before failing.

Fortunately, Windows happens to be a good operating system and good OS's stop your program from eating up all the ram. It got to 2GB (which is my pagefile allowance) before it crashed on a bad memory allocation.

Chapter 17 // Exercise 5 - Principles & Practice Using C++

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

Chapter 17 // Exercise 5

Write a function, char* findx(const char* s, const char* x), that finds the first occurrence of the C-style string x in s.

Github: https://github.com/l-paz91/principles-practice/blob/master/Chapter%2017/Exercise%205

I'm not entirely sure what he meant by this so I interpreted it as "finds the first occurrence of the C++-style string in the C-Style string".

Also, he did not specify not to use the standard library on this one. There is already the function strstr() to do this that takes in two const char*. 

http://www.cplusplus.com/reference/cstring/strstr/

The actual definition of this function though is deep in the bowels of VS runtime string headers but it basically takes in two pointers to the start of the char arrays and then returns a pointer to the start of the occurrence. This means that if you print the pointer, it will print everything starting from that occurrence.

I mimicked this behaviour and also cast that const away (just like the standard library does).

Chapter 17 // Exercise 4 - Principles & Practice Using C++

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

Chapter 17 // Exercise 4

Write a function, char* strdup(const char* c), that copies a C-style string into memory it allocates on the free store. Do not use any standard library functions.

Github: https://github.com/l-paz91/principles-practice/blob/master/Chapter%2017/Exercise%204

With const pointers I find it really stupid that you can't change the object that the pointer is pointing at, but you can change what the pointer is pointing at. In this exercise, c can be changed to point at some random garbage address but god forbid you want to assign the pointer to a non-const pointer. Unreal has a problem with this because pretty much everything gets passed round as const pointers but this allows for people to change what it's pointing at and no one will be none the wiser because it says const in the argument parameters. A lot of programmers assume (and rightly so) that this means their arguments won't be modified in the function body.

We have a senior engineer who prefers us all to use const references as you cannot change the object OR change what it's pointing at and less mistakes can be made.

Also, strdup() is a deprecated std library function so I renamed it so it would compile.

Chapter 17 // Exercise 1, 2, 3 - Principles & Practice Using C++

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

Chapter 17 // Exercise 1, 2, 3

1. What is the output format of pointer values on your implementation? Hint: don't read the documentation.

2. How many bytes are there in an int? In a double? In a bool? Do not use of sizeof except to verify your answer.

3. Write a function, void to_lower(char* s), that replaces all uppercase characters in the C-style string s with their lowercase equivalents. For example, Hello, World! becomes hello, world!. Do not use any standard library functions. A C-style string is a zero-terminated array of characters. So if you find a char with the value 0 you are at the end.

Github: https://github.com/l-paz91/principles-practice/blob/master/Chapter%2017/Exercise%203

1. Addresses are printed in capitals as "010FFA44", so in hex without the 0x prefix.

2. At least on my pc an int is 32 bits (4 bytes), a double is 64 bits (8 bytes) and a bool is 8 bits (1 byte). I'm not sure if he wanted us to verify this?

3. I used some of my assembly knowledge to do this. ASCII is very clever and well thought out. When it comes to letters, lowercase characters always have their 5th bit set to 1 and uppercase characters have it set to 0; so you can easily switch between upper and lower by just inverting bit 5.

That's what I did here:

On line 22, we access the contents of s, then OR bit number 5 with 1. As uppercase are 0 in bit 5, when you OR 0 with 1, you get 1, so it flips the upper character to lower.

This does not affect already lower case letters or punctuation (as 1 OR 1 is 1). Some more examples:

You can also use char ^= (1 << 5) to toggle the bit instead of setting it once.

A warning; s will now be pointing at the end of the array. You can also do while(s[i] != 0; ++i) to avoid this (where i is the length of the array) or assign the pointer to another pointer for the function.