I have a declaration of an array like
int a1[5];
If I declare this array like this:
int *a2;
a2 = malloc(sizeof(int)*5);
and then use it as I would use the array a1 what are the differences. Also if this is done in a function and the function ends both a1 and a2 go out of scope. In case of a1 the memory is released automatically but in case of a2 is it done automatically or would we have to deallocate it using delete?
When you write
int a[10];
you say
"assign 10 blocks of memory to me each of which can store an integer value".
By default when you put this definition in a block (part of code surrounded by { and }), you cannot use the variable a outside of block.
Why? Suppose the program is executing instructions inside of a block and it came across this definition. It allocates some memory to store the variable a. When the program finds that it has reached the end of block, it destroys the whole memory it has allocated while it was in the block. So, when you refer a in code after the closing brace (}), it doesn't know what a is because the memory was destroyed.
On the other hand when you write
int* a = (int*) malloc(10*(sizeof(int)));
you say
"assign 10 blocks of special memory to me each of which can store an integer value"
. This special memory is called heap memory. It is special because, it is present in a new place that is never destroyed (unless you ask it to). So, you can access it even outside the block.
a2's memory won't be deallocated automatically. You can always follow this simple rule of thumb - if you used malloc to allocate it, you need to use free to deallocate it.
