memory allocation

[cAsk]

hi. do i have to always allocate memory when i use arrays? for instance, i need to use an array of ints where length is a variable. i wrote "int a[n];" should i change it to "int a[n] = malloc(sizeof(int)*n);"?

[laserlight]

do i have to always allocate memory when i use arrays?

Of course, but if you just define:

int a[N];

where N is a constant, then memory will be allocated, but you need not worry about manually managing the memory.

i need to use an array of ints where length is a variable. i wrote "int a[n];" should i change it to "int a[n] = malloc(sizeof(int)*n);"?

If you are compiling with respect to C99, or with respect to C11 where the feature is supported, or with respect to an earlier version of C where the feature is available as a language extension, then you can use variable length arrays, e.g.,

int a[n];

where n is not a constant. However, such an array cannot be resized during its lifetime. Furthermore, because of the caveats about compiler support, you may choose to use the two other more portable options:

• Allocate an array as large as you will ever need, then use as much as you need. Unfortunately, this may result in a colossal waste of space.
• Use dynamic memory allocation with malloc/free and related functions. This allows you to resize the dynamic array with realloc. However, you would need to declare a pointer, not an array, e.g.,
  

  int *a = malloc(sizeof(a[0]) * n);

  and then you should check that malloc did not return a null pointer, and remember to free.

[cAsk]

thanks for the ellaborated and quick response
btw, yes i use C99

[CodeSlapper]

You could also use

Int *a = malloc(sizeof(*a) * n);