can we declare a variable inside an array

Question

#include <stdio.h>

int main () 
{
    int size,i;
    int arr[size];

    printf ("Enter size of array\n");
    scanf ("%d",arr[size]);

    for (i=0; i<=size; i++)
    {
        printf ("%d", arr[size]);
    }

    return 0;
}

You can't create an array of size determined at runtime this way. `size` must be a literal - not a variable typed in by the user. — i spin and then i lock, Dec 03 '21 at 14:51
`size` is of size unknown, you must assign value before using to define size of an `array`. — TruthSeeker, Dec 03 '21 at 14:52
@kenticent maybe this help: https://en.wikipedia.org/wiki/Variable-length_array — justANewb stands with Ukraine, Dec 03 '21 at 14:55
@kenticent, C99, [refer](https://en.cppreference.com/w/c/language/array) — TruthSeeker, Dec 03 '21 at 14:57
@justANewbie I was hinting that VLA is in the first place a C99 feature, which is not obligatory in the further standards. On the Wikipedia it is said, that "In C11, a __STDC_NO_VLA__ macro is defined if VLA is not supported.", therefore I'm asking, which standard does OP use. — i spin and then i lock, Dec 03 '21 at 14:59
Possible duplicate of [Dynamic array allocation on stack in C](https://stackoverflow.com/questions/26441916/dynamic-array-allocation-on-stack-in-c) — Wyck, Dec 03 '21 at 15:07
Using a VLA is (IMHO) the least of the problems present in this code. — n. m. could be an AI, Dec 03 '21 at 15:20

score 3 · Answer 1 · edited Dec 03 '21 at 15:18

I have not understood the question but your code is invalid.

Before declaring the variable-length array arr the variable size must to have already a positive value. So you need to write at least like

int size,i ;

printf ("Enter size of array\n") ; 
scanf ("%d", &size) ;

int arr[size] ;

This call of scanf

scanf ("%d",arr[size]);

does not make any sense, not least because the second argument of the call must be a pointer.

Also, the condition in the for loop must look like

for (i=0; i <size; i++) {
          ^^^^^^^

And you are trying to output a non-existent element of the array

printf ("%d", arr[size]);

The valid range of indices for this variable-length array is [0, size).

It seems you mean

printf ("%d ", arr[i]);

But before outputting elements of the array you need to assign values to them because the array is not initialized and you may not initialize a variable-length array at its declaration.

can we declare a variable inside an array

1 Answers1