When only a copy of an argument is passed to a function, it is said to be passed by _________.

When only a copy of an argument is passed to a function, it is said to be passed by value.

Value

Functions are used to provide $\textbf{behavior abstraction}$ to a $\textit{sequence of steps}$ being performed over and over again, yet with different starting values. It is crucially important when further development. As a case study, consider you provide a sequence of $\textit{summing two values}$, for instance. If you $\textit{hard-coded}$ the operation that performs the addition every time you want it, you would end up with various $\textbf{unnecessary}$ steps that exactly do the same thing, but within different areas of your program. This would make your program $\textit{more complex}$. Moreover, if you ever wanted to modify a piece of code that is used to perform the addition, you would have a nightmare reviewing $\textbf{every situation}$ and fixing it appropriately. Unlike this situation, you would have fixed the code only once in the case of a function.

Functions have an $\textbf{exact number}$ of parameters; they are separated with $\textit{commas}$ `,'. The $\textbf{order}$ of the passed arguments $\textit{matters}$---you should call the function with a matching order to the declared types. Furthermore, there are two $\textit{types of parameters}$, passing them:

$\bullet$. Value parameter, $\boxed{\text{pass by value}}$: it is a type of parameters of the functions where changes to it are kept local, so changing them would not affect the actual calling values. This is because the values are copied during the call, so any modification happens to the $\textbf{copy}$ rather than the original value. $\bullet$. Reference parameter, pass by $\textit{reference}$: it is a type of parameters of the functions where changes to it are reflected globally, so changing them will affect the actual calling values. This is because the value are not copied anymore; therefore, any changes would be applied to the original values.