Function delcarations are very significant, as you must define what the return type of the function is. A void function doesn't need a return type, whereas the int function must have an integer value as its return type.

It is very important when creating a function to select the return type. If you want your function to return an integer, you would place "int" before your function to signify that the function expects an integer output. In this case, the function is declared as void, meaning there is no output. However, the code indicated a return value of 2, which conflicts with the void keyword. To fix this problem, either remove the return statement or change void to int.

In our problem, the program has to run AT LEAST ONCE in order to present all of the options to the user. Because of this reason, the best option is a do-while loop because the statements within that loop execute at least one time and the condition to get out of the loop is at the end. In this case, the exit condition would be if the user presses quit (after the options have been shown at least once).

A while loop might work in this case; however it is not necessarily the smartest option. This is because the condition is tested before anything is executed within the loop. This means that whatever is inside the while loop does not necessarily have to be executed at all.

A for loop is also not a good option for this problem because a for loop is executed a set amount of times. In this case, we don't know if the user is going to want to do 1 transaction or 10. Therefore, a for loop is not the best choice.

An infinite loop is also not what we want because it runs forever. In our case, we want the code to stop prompting the user and end after "quit."

Pointers store the address of another variable. Pointers are declared by naming the type, then an asterisk, followed by the name of the variable. In our example, var1 was declared a pointer that points to an integer:

int * var1;

Next in the code, we see that an integer variable named "foo" is created and is assigned a value of 63.

The address-of operator (&) is then used to get the address of a variable. Now lets take a look at the next line of the code:

 var1 = &foo;

Here the ampersand is used to get the address of foo within memory. This means that var1 contains the address value of where foo is stored in memory.

Next in the code, we have the following statement:

var2 = *var1;

Here the dereference operator (*) is being used. This operator is used whenever we want to get the value (not the address) of the variable that a pointer is pointing to. In this case, var1 is storing the address of foo. However, by using the dereference operator we can get the actual value of the variable whose address is being stored in var1. In this case, dereferencing var1, we get the actual value of foo which is 63. Therefore, var2 = 63.

When a two dimensional array is created and initialized, the way to access the items inside the matrix is by calling the array with the row and column (i.e. myArray[ROW][COLUMN]). Keeping in mind that arrays start at 0, the number four would be in row 1, column 0. Therefore to save that number into the variable "fourth" we'll do the following:

fourth = myArray[1][0];

*Note: myArray[1][0] is not the same as myArray[0][1].

myArray[1][0] =4 because it is the item located at row=1 and column = 0. 

myArray[0][1] =12 because it is the item located at row=0 and column = 1. 

Hash map - key being title and value being the number of copies

Hash maps are a collection of (key, value) pairs.

Hash maps have O(1) access, so this would be the quickest and best way to store the data. 

Arrays can be two-dimensional. However, when trying to keep track of keys and values it can become complicated when using an array. HashMaps are the best way to represent data containing keys and values. 

In Java, the only way to write functions is to make them class methods. Java does have primitive types int, boolean double. There is compile time error checking. Java is an Object Oriented langauge and supports the OO paradigm. There is automatic garbage collection support, which helps manage memory for the user.