Can the size of an array be declared at runtime?

No. In an array declaration, the size must be known at compile time. You can�t specify a size that�s known only at runtime. For example, if i is a variable, you can�t write code like this: char array[i]; /* not valid C */ Some languages provide this latitude. C doesn�t. If it did, the stack would be more complicated, function calls would be more expensive, and programs would run a lot slower. If you know that you have an array but you won�t know until runtime how big it will be, declare a pointer to it and use malloc() or calloc() to allocate the array from the heap.

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M. PAVAN KUMAR REDDY

Jan 18th, 2007

If you need this type of behavior, you have to use dynamic memory.
You can try this:
void main()
{
    int *ptr = NULL;
    int arr_size;
    printf("Enter the size of array : ");
    scanf("%d",&arr_size);
   ptr = (int*) malloc(arr_size*(sizeof(int));
}
Then you can use ptr as just like an array. If you wish to initialize array, you can initialize using ptr[0], ptr[1], ptr[2]....