What is the difference between passing an array and passing single value data to a function?

Answer 1

Passing a single value to a function is often just a simple integer. But passing an array, character string or other data structure is typically "pass by reference", or in other words, the calling statement will 'point to' the place in memory where the data structure resides.
When a function is called using a pointer to a data structure, both the calling environment and the called function are referencing the same data; any changes made to the data in the structure by the function will have changed the data that the original calling environment sees.
However, when a value is passed to a function, the function creates it's own copy of the value, and can change it in any way without changing the original value.