is it mandatory that in assigning we should mention array size while writing program

Question

In let us C it is mentioned that "while assigning an array we have to commit to the size of the array at the time of writing the programs". But in the code below I'm giving the size at the time of execution still it's working so which is correct ?

code :

#include <stdio.h>
void main(){


{
    int n,i;
    printf("give the size of the array \n");
    scanf("%d",&n);
    int  a[n];
    printf ("give array elements\n");
    for (i=0;i<n;i++)
    {
        scanf("%d",&a[i]);
    }
}

It is said here: https://stackoverflow.com/questions/562303/the-definitive-c-book-guide-and-list that the book you are using "is a horribly outdated book that teaches Turbo C and has lot of obsolete, misleading and downright incorrect material". — babon, Dec 18 '17 at 11:50

score 2 · Answer 1 · answered Dec 18 '17 at 11:46

2

That's a variable-length array and is perfectly valid in C (since the C99 standard).

You should probably update your books. Here's a list of good ones.

answered Dec 18 '17 at 11:46

Some programmer dude

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score 0 · Answer 2 · answered Dec 18 '17 at 11:46

First of all, I think you meant declaration instead of assignment.

That said, this is called variable length array or VLA. It's a C99 onwards addition.

Quoting C11, chapter §6.7.6.2/P4

If the size is an integer constant expression and the element type has a known constant size, the array type is not a variable length array type; otherwise, the array type is a variable length array type.

is it mandatory that in assigning we should mention array size while writing program

2 Answers2