$(2$ pts$)$ Part $2$: Understand References and Pointers

In part $2,$ you will be working in a group to review the references in C$++,$ and we will introduce the concept of pointers.

Files needed for this part: sentence.cpp Revisit references:

Suppose our main function is as follows:

int main$()\{$

string sentence;

get$\_$sentence$($sentence$)$;

cout $<<$ sentence $<<$ endl;

return $0$; $\}$

In last lab, we know that in order to change the value of the string sentence inside the get$\_$sentence$()$ function, we need to add an ampersand $($&$)$ in front of the parameter. This is called pass by reference, i$.$e$.,$ by using the following function:

$1$

void get$\_$sentence$($string &s$)$;

The reference variable s in the parameter list refers to the memory location of the argument, sentence. Therefore, if we update s in get$\_$sentence$()$ function, sentence in main$()$ will be changed as well. This is accomplished by using a very important concept implicitly, pointers.

Introduction to Pointers

In C$/$C$++,$ pointers are powerful entities that allow you to manage memory and manipulate data directly.

A pointer is a variable that holds the memory address of another variable.

To declare a pointer, use the data type followed by an asterisk $(*)$ and the pointer name. For example: int number $=42$;

int $*$ptr $=$ &number; $//$Declare and Initialize ptr with the address of 'number' Now, our pointer variable, ptr$,$ holds the memory address of number.

$($Note$,$ you may use &var to get the memory address of var$)$

To access$/$update the value stored at the memory address pointed to by a pointer, use the dereference operator $(*).$ For example:

cout $<<*$ptr $<<$ endl; $//$ the value of $$number$$ will be printed, which is $42*$ptr $=50$; $//$number$$ is changed to $50$

Since reference variables is only available in C$++,$ you are still required to understand how to use pointers to achieve the same goal. Now, change the function prototype to:

void get$\_$sentence$($string $*$s$)$;

Answer the following questions:

$1.$ Can the value of the string $($sentence$)$ be changed with the modified function prototype? If so$,$ how? $2.$ Compared to using reference variables, what other modifications are required when making the function call and inside the function?

$3.$ What is the difference between an ampersand $($&$)$ and an asterisk $(*)$ added in front of the parameter? Use a diagram to explain.