Assignment 2: An Object-oriented Dynamic String Array


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Assignment 2: An Object-oriented Dynamic String Array

Your task is to use *object-oriented programming* to implement a vector-like
class called `str_vec`. One of it’s major features is that it completely (and
correctly!) manages its own memory, similar to a `vector<string>`.

## Getting Started

Put all your code for this assignment into [a2.cpp](a2.cpp). Implement all the
requested methods and functions using the *exact* name and parameters. You can
add other helper functions/methods if you need them.

Write a test function to automatically test *each* major method/function to
ensure it is correct. Use either if-statements or assertions for the testing.
Each test function should have approximately 5 tests (more complex/input code
should probably have more).

## Questions

Implement each of the following methods and functions. Use `const`, `public`,
and `private` whenever possible.

1. Implement a **default constructor** for `str_vec()` that creates a new
`str_vec` of size 0 and capacity 10.


str_vec arr;
// arr is an empty str_vec of size 0 and capacity 10

The capacity of `str_vec` is the size of its underlying array. The size is
the number of items in the `str_vec` from the point of view of the user.

2. Implement a **destructor** `~str_vec()` that deletes the dynamic memory used
by the `str_vec`.

Be sure your program has no memory leaks by testing it with `valgrind`!

3. Implement a **constructor** `str_vec(n, s)` that creates a new `str_vec` of
size `n` where each element is a copy of the string `s`. The capacity should
be at least `n`. If `n` is less than 1, use `cmpt::error` to throw a helpful
error message.


str_vec arr(5, “cat”);
// arr is str_vec of size 5, each entry containing the string “cat”

4. Implement a **copy constructor** `str_vec(other)` that creates a new
`str_vec` that is a copy of the `str_vec` `other`.


str_vec a(5, “<empty>”);
str_vec b(a);
// b is a str_vec of size 5 with each entry equal to the string “<empty>”

The *capacity* of `b` should be at least the *size* of `a`.

Both `a` and `b` should have their own underlying array.

5. Implement an **array constructor** `str_vec(arr, n)` that creates a new
`str_vec` that is a copy of the array of strings named `arr`, with size `n`.
The type of `arr` in the constructor is `const char*[]`.


const char* arr[] = {“red”, “white”, “yellow”};
str_vec a(arr, 3); // 3 is the length of arr
// a is a str_vec of size 3 with entires “red”, “white”, “yellow”

The passed-in array should not be changed in any way. `a` should have its own
copy of `arr`.

6. Implement these **getters**:

– `size()` and `length()`: both return the number of strings in the
`str_vec`. Two methods are provided for returning the size as a
convenience: `length()` is an alias for `size()`.

– `capacity()`: returns the capacity of the `str_vec`, i.e. the size of the
underlying array.

– `pct_used()`: returns the percentage (from 0.0 to 1.0) of the underlying
array that is in use, i.e. the size divided by the capacity.

Make sure that these are all `const` methods!


str_vec empty;

cout << empty.size() << ‘ ‘ // 0
<< empty.capacity() << ‘ ‘ // 10
<< empty.pct_used() << ‘\n’; // 0

Write three test functions, one for each method.

7. Implement these non-mutating methods:

– `to_str()`: returns a `string` representation of the `str_vec`. Each string
should be printed in “-quotes, and wrapped in {}-braces as shown in the
example below.

– `print()`: a `void` method that prints the string representation of the
`str_vec` to `cout` *without* a `\n` at the end.

– `println()`: a `void` method that does the same thing as `print()`, but
also prints a `\n` at the end

Make sure these are all `const`!


str_vec arr(3, “cat”);

string s = arr.to_str(); // s is the string {“cat”, “cat”, “cat”}

arr.print(); // prints {“cat”, “cat”, “cat”} on cout (no \n at end)
arr.println(); // prints {“cat”, “cat”, “cat”} on cout (\n at end)

For this question you only need to make a test function for `to_str()`. For
this assignment, it’s okay if you check the results of `print` and `println`

8. Implement these methods:

– `get(i)` is a **getter** that returns the `string` at index location `i` of
the `str_vec`. Just as with arrays, the first index location is 0. Make
sure this is `const`!

– `set(i, s)` is a **setter** that sets index location `i` to be a copy of
string `s`.

Both methods should do *bounds checking*: use `cmpt::error` to throw a
helpful error message if the passed-in index `i` is less than 0, or greater
than `size() – 1`.


str_vec arr(3, “cat”);

arr.set(1, “dog”); // arr is now {“cat”, “dog”, “cat”}

string s1 = arr.get(1); // s1 is “dog”
string s2 = arr.get(2); // s2 is “cat”

Write test functions for both `set` and `get`.

9. Implement these mutating methods:

– `append(s)` is a `void` method that adds the string `s` to the right end
(the back) of the `str_vec`, increasing the size by 1.

– `append(sv)` is a `void` method that appends *all* the strings in the
`str_vec` `sv` to the right end (the back) of the `str_vec`, increasing the
size by the size of `sv`.

For both methods, the underlying capacity should only be increased if
necessary. When the capacity is increased, it should be *doubled*.


str_vec arr; // {}
arr.append(“apple”); // {“apple”}
arr.append(“orange”); // {“apple”, “orange”}

str_vec fruit; // {}
fruit.append(“pear”); // {“pear”}
fruit.append(“banana”); // {“pear”, “banana”}

arr.append(fruit); // {“apple”, “orange”, “pear”, “banana”}

arr.append(arr); // {“apple”, “orange”, “pear”, “banana”,
// “apple”, “orange”, “pear”, “banana”}

Write two test functions, once for each version of `append`.

10. Implement the `void` mutating method `capitalize_all()` that *capitalizes*
all the strings in `str_vec` that can be capitalized. A string can be
capitalized if it is *not* empty, and the first character is one of the 25
lowercase letters a to z. Strings that can’t be capitalized are left

For example, if the `str_vec` `a` is `{“hat”, ” dog”, “house boat”,
“Wall”}`, then after calling `a.capitalize_all()` it will be `{“Hat”, ”
dog”, “House boat”, “Wall”}`.

This is a mutating method, so the `str_vec` itself should be changed (no
copies made).

11. Implement the `void` mutating method `remove_first(const string& s)` that
removes the *first* occurrence of `s` in the `str_vec`. All the strings to
the right are moved left one position to fill in the gap, and the size of
the `str_vec` is decreased by 1. If `s` is not in the `str_vec`, then the
`str_vec` is unchanged.

For example, if `str_vec` `a` is `{“hat”, “shoe”, “hat”}`, then after
calling `a.remove_first(“hat”)`, it will be `{“shoe”, “hat”}`.

12. Implement the `void` mutating method `keep_all_starts_with(char c)` that
*keeps* only strings that start with `c`, and removes any others.

For example, if the `str_vec` `a` is `{“hat”, “book”, “horse”, “house”,
“Hot!”}`, then after calling `a.keep_all_starts_with(‘h’)` it will be
`{“hat”, “horse”, “house”}`.

The order of the strings after calling `keep_all_starts_with` should be the
same as before calling it.

If none of the strings start with `c`, or the `str_vec` is empty, then
then the `str_vec` is empty after calling `keep_all_starts_with`.

13. Implement these mutating methods:

– `clear()` is a `void` method that removes all elements from the
`str_vec` so its size is 0. Make this method as efficient as possible.
The capacity can stay the same.

– `squish()` is a `void` method that will, if necessary, re-size the
underlying array so that the size and capacity are the same. The
elements in the array are the same (and in the same order) after
squishing as before.


str_vec arr; // {}, size 0, capacity 10
arr.append(“a”); // {“a”}, size 1, capacity 10
arr.append(“b”); // {“a”, “b”}, size 2, capacity 10

arr.squish(); // {“a”, “b”}, size 2, capacity 2

arr.clear(); // {}, size 0, capacity 2

Write test functions for both `squish` and `clear`.

14. Implement these functions (*not* methods!):

– `operator==(a, b)` is a `bool` function that returns `true` if the
`str_vec` `a` and the `str_vec` `b` have the same elements in the same
order, and `false` otherwise

– `operator!=(a, b)` is a `bool` function that returns `true` if the
`str_vec` `a` and the `str_vec` `b` *don’t* have the same elements in
the same order, and `false` otherwise


str_vec a(3, “cat”);
str_vec b(3, “cat”);

if (a == b) cout << “same\n”; // prints “same”
if (a != b) cout << “different\n”; // prints nothing

a.set(0, “feline”);

if (a == b) cout << “same\n”; // prints nothing
if (a != b) cout << “different\n”; // prints “different”

Write test functions for both `operator==` and `operator!=`.

15. Implement a mutating method `sort()` that re-arranges the elements of a
`str_vec` into alphabetical order.

For example:

str_vec a;

cout << a.to_str() // {“hat”, “dog”, “cat”, “house”}
<< “\n”;
cout << a.to_str() // {“cat”, “dog”, “hat”, “house”}
<< “\n”;

This is a mutating method, so the `str_vec` itself should be changed (no
copies made).

## Submit Your Work

Please put all your code into [a2.cpp](a2.cpp), and submit it on
[Canvas]( Implement **all** the methods and functions exactly as
described, otherwise the marking software will probably give you 0!

Submit only [a2.cpp](a2.cpp), and no other files. The marker will use the
standard [makefile](makefile) to compile it, and a copy of
[cmpt_error.h](cmpt_error.h) will be in the same folder as [a2.cpp](a2.cpp) when
it’s tested.

## Basic Requirements

Before we give your program any marks, it must meet the following basic

– It must compile on Ubuntu Linux using the standard course

$ make a2
g++ -std=c++17 -Wall -Wextra -Werror -Wfatal-errors -Wno-sign-compare -Wnon-virtual-dtor -g a2.cpp -o a2

If your program fails to compile, your mark for this assignment will be 0.

A copy of [cmpt_error.h](cmpt_error.h) will be in the same folder as
[a2.cpp](a2.cpp) when it’s compiled, so your program can use `cmpt::error`
if necessary.

– It must have no memory leaks or memory errors, according to `valgrind`,

$ valgrind ./a2

// … lots of output …

A program is considered to have no memory error if:

– In the `LEAK SUMMARY`, `definitely lost`, `indirectly lost`, and `possibly
lost` must all be 0.

– The `ERROR SUMMARY` reports 0 errors.

– It is usually okay if **still reachable** reports a non- zero number of

– **You must include the large comment section with student info and the
statement of originality**. If your submitted file does not have this, then
we will assume your work is not original and it will not be marked.

If your program meets all these basic requirements, then it will graded using
the marking scheme on Canvas.

## Hints

– In [a2.cpp](a2.cpp), there is the commented-out function `austenTest()` that
you may choose to use to help test your class when it’s done. You don’t need
to use it, and you can change it if you like.

## Marking Scheme

### **Overall source code readability: 5 marks**
– All code is sensibly and consistently indented, and all lines are 100
characters in length, or less.
– Whitespace is used to group related pieces of a code to make it easier for
humans to read. All whitespace should have a purpose.
– Variable and function names are self-descriptive.
– Appropriate features of C++ are used, as discussed in class and in the notes.
**Note** If you use a feature that we haven’t discussed in class, **you must
explain it in a comment**, even if you think it’s obvious.
– Comments are used when needed to explain chunks of code whose purpose is not
obvious from the code itself. There should be *no* commented-out code from
previous versions.

### **Overall source code performance and memory usage: 2 marks**
– No unnecessary work is done.
– No unnecessary memory is used.

### **Source code correctness**
To get full marks, your functions must pass all the test cases the marker uses
for that question. The marker may use test cases not given in the assignment.

– **Question 1-15**, **2 marks** each. 1 mark for the correct method/function,
and 1 mark for a good testing function for that method/function.

A few of the questions have more than one function/method, and you should
write a test function for each.

### Deductions
– **-1 mark** (at least) if your file does not have the correct name, or you
submit it in the incorrect format.
– up to **-3 marks** if you do not include your full name, email, and SFU ID in
the header of your file.
– **a score of 0** if you don’t include the “statement of originality in the
header of your file.
– **a score of 0** if you accidentally submit a “wrong” non-working file, and
then *after the due date* submit the “right” file. If you can provide evidence
that you finished the assignment on time, then it may be marked (and probably
with a late penalty).

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