Homework 3 - MyString

2020_S19/wk3/hw3.cpp

Assignment

The purpose of this assignment is to learn how to manipulate member variables that are dynamic arrays, how to use operators with dynamic array member variables and how to create a small abstract data type (ADT).
You will be making your own implementation of a string class called MyString.
Your string class will not only implement the dynamic array functions such as a destructor, it will also dynamically reallocate itself when it runs out of space. For example, if the string only has room for three more characters and the user appends 10 characters, you will reallocate the string so it has enough space for all the characters.
Your MyString class will be an abstract data type, so all member variables and helper functions need to be private. Additionally, you should use comments to describe each public member function.
Your string class will have the following member variables:

• A character pointer for the string
• An integer for the number of characters currently allocated to the string (e.g. the total capacity of the string)
• (Optional) An integer for the number of characters in the string (e.g the string length). This is optional because strlen will also tell you the number of characters in a string.

• Default constructor - Allocate a character array that can hold a string with 21 characters (20 characters plus the null character). Make this new array the empty string by setting the first character to the null character.
• Copy constructor - Allocate a character array based on the source's capacity and copy the source string over into that array.
• Destructor - Deallocate the array if it is allocated.
• Conversion constructor for a single character - Allocate a character array that can hold a string with 20 characters (plus the null character) like the default constructor. Then assign the passed character to the first slot in the array and also set the null character.
• Conversion constructor for a C-style string (character array) - Allocate a character array large enough to hold the passed C-style string (plus the null character). Then copy the characters from the passed array into the class's array.
• Assignment operator (=) - Copy the string of the source into the current string, deleting anything the current string may contain. Only reallocate if your current character array does not have the capacity to hold the source string. Important: make sure you check for 'a = a' (e.g. trying to assign oneself to oneself) and return out of the function without doing anything if that happens.
• Input operator (>>) - It will replace the current string with the first word (up to the first whitespace) on the input stream. You may need to reallocate the character array if there are more characters on the input stream before the first whitespace than the array can hold.
• Output operator (<<) - If the string exists, output the string to the output stream. Otherwise, output the empty string ("").
• Concatenation operator (+) - Return a new string that is the left operand followed by the right operand (i.e. "Hello "+"world" would return "Hello world"). Your temporary string object within the operator needs to have a capacity large enough to hold left's characters, right's characters and the null character.
• Append operator (+=) - Append the contents of the right hand operand to the current string. You may need to resize the character array in the current object so that it has enough capacity to hold the new string.
• Index operator ([ ]) - Return the character at the specified index if the string exists. If the index is invalid, exit out of the program.
• Less than operator (<) - Return true if the left string is lexiographically less than the right string. Hint: strcmp()
• Greater than operator (>) - Return true if the left string is lexiographically greater than the right string. Hint: strcmp()
• Equality operator (==) - Return true if the two strings have the same characters. Hint: strcmp()
• Inequality operator (!=) - Return true if the two strings differ for any character. Hint: strcmp()
• int length() - Returns the current length of the string. If the string exists, return strlen() function. Otherwise, return 0.
• void erase() - Deletes the string. You may either delete the memory allocated or set the first character to the null character.
• void getline(istream &in, int size) - Get size - 1 characters from the input stream and store it in the current string object, replacing the current string. If size is greater than the current capacity, reallocate the array to be able to hold count characters.

Additional Notes and Requirements

The capacity member variable contains the amount of the memory allocated, not the length of the string. Use the length() member function (or the optional length member variable) to get the current string length. The current string length may be smaller than the amount of memory allocated in certain situations. This is perfectly fine. The length should NEVER be greater than the capacity.
For append (+=), if the current string is does not have enough memory allocated to store itself plus the appended string, you must allocate a new string that is long enough. In this process, you have to save the contents of the current string so that you can copy it over to the new string. Do not forget to save the current string before reallocating, if you need to reallocate.
For assignment (=), input (>>) and getline(), if the current string is not long enough to store the source string, delete the current string and allocate enough space. Unlike +=, you do not need to store the current string as it will be completely replaced by the new string. Also, do NOT point the character pointer of the current object to the character pointer of the source. Copy the data over to the current object's own array using a for() loop or strncpy().
The copy constructor and the constructor that takes a C-style string will allocate an array large enough for the source string and copy the string over to its array. Do NOT point the character pointer of the current object to the character pointer of the source. Copy the data over to the current object's own array using a for() loop or strcpy().

Main function

The value of a is: 
The value of b is: Hello
The value of c is: r
The value of clone is: Hello
Enter a new word for c: John
The value of c is: John
Concatenation (b+clone): HelloHello
Assignment (a=b): Hello
Append (a+=c): HelloJohn
The value of a[0] is H
Equality (b==clone) is true.
Inequality (b!=c) is true.
Less than (a<b) is false.
Greater than (c>b) is true.
a's length is 9
After erase(), a's length is 0
Enter a new string for a (100 chars max): John Doe
You entered: John Doe