Implement the following string methods in DynamicString.cpp:

DynamicString$()//$ Constructs an empty string. Allocating enough memory to store the null character

DynamicString$($const char$*$ str$)//$ Constructs a string by copying the characters from the char array str to this object. You should dynamically allocate enough memory for the entire string.

DynamicString$($const DynamicString& other$)//$ Constructs a string by copying the characters from the "other" DynamicString object. You should dynamically allocate enough memory for the entire string.

~DynamicString$()//$ Deletes the memory used for storing the char array since this DynamicString object is being destroyed.

DynamicString& operator$=($const DynamicString& other$)//$ Deletes the memory previously used for storing the char array and creates a new array. The characters from the "other" DynamicString are copied into this array.

int len$()$ const $//$ Returns the length of this string $($i$.$e$.$ the number of characters in the array not including the null char$)$

const char$*$ c$\_$str$()$ const $//$ Returns a pointer to the underlying char array

char char$\_$at$($int position$)$ const $//$ Returns the char at the specified position

char& operator $//$ Returns the char at the specified position

bool startsWith$($const DynamicString& other$)$ const $//$ Returns true if other is a prefix of this string

bool endsWith$($const DynamicString& other$)$ const $//$ Returns rue if other is a suffix of this string

int compare$($const DynamicString& other$)$ const $//$ Returns a negative integer if this is less than other, $0$ if this is equal to other, and a positive integer if this is larger than other. Note that for strings, $"$a$"$ is less than $"$b$",$ as $"$a$"$ comes in the dictionary before $"$b$".$ Likewise $"$a$"$ comes before $"$aa$"$ in the dictionary. Computer case sensitivity also applies which naturally makes $"$A$"<"$a$".$

DynamicString& toLower$()//$ Converts the string to lowercase

DynamicString& toUpper$()//$ Converts the string to uppercase

DynamicString& replace$($char old, char new$)//$ Replace all instances of old with new

int find$($char needle, int start$=0)$ const $//$ Return the first index of the specified char or $-1$ if the char is not found starting from index start.