Dynamically create an array?

[Unknowntoyou000]

I was given a programming assignment.. and part of it states:
"
1. Read how many students are in the file and dynamically create an array of structure to store the student information.
"

I'm not sure what is meant by dynamically create an array?

[laserlight]

You should use a std::vector, or if that is not allowed, dynamically allocate arrays with new[] and delete[] them when you are done.

[Unknowntoyou000]

ok thanks (:
the new[] and delete[] I believe is what my professor was referring to

[rudyman]

Dynamically allocating memory just means you're storing data without knowing (necessarily) how much data you need to store. It also gives the memory indeterminate scope.

Here's how you create a regular array: (You're probably very familiar with this)

int my_array[5]; // array of 5 integers

Here's how you dynamically create an array:

int* my_array = new int[5];

Note that the number in brackets (the 5 in this case) can be a variable.

When you're done using that memory:

delete [] my_array;

The reason you'd want dynamic allocation here is because the number of students in the file is variable.

[master5001]

Same teacher? http://cboard.cprogramming.com/showthread.php?t=102265

I think there are more efficient ways of doing this, but I am certain none of them are what your teacher was searching for (bar none, using the stl vector class is the best all-around solution).

In either event, refer the your classmate's(?) link... Though next time it wouldn't hurt to read other threads before posting. His post has never been more than a couple posts lower than yours on the forums.

[Unknowntoyou000]

so I'm trying to dynamically create this array of structures...

should it look something like:

struct* my_array = new my_struct[x];

where x is the number of students
?? or what?? .. I don't really know -_-''

[vart]

more likely

my_struct* my_array = new my_struct[x];

[master5001]

Click the link I posted above. This person is trying to accomplish the same thing.

 struct my_struct* my_array = new my_struct[x];

^ That one will even compile too

[vart]

Click the link I posted above. This person is trying to accomplish the same thing.

struct is optional in C++

[iAmFedor]

^^^^ nobe question but is that not creating a pointer to an array?

[vart]

dynamic array IS a pointer to the first element

[iAmFedor]

so in c++ you cant just create a dynamic array?

int myAry[x];

[laserlight]

so in c++ you cant just create a dynamic array?

Not in that way. Standard C++ does not support variable length arrays.

[master5001]

struct is optional in C++

Indeed, however I think its a good idea to illustrate why the OP wasn't totally off.

[iAmFedor]

Ok another question..........

Sorry dont want to be annoying but i find it so much easier to code when i understand how things work.

What is the difference that creating a pointed to the array allows you to make a dynamic array?