Array declaration problem in C with variables

Question

Is this allowed in C Language as given below:

int a=2, b=3;
int arr[a+b];

Is this a valid C statement?

• interjay: This isn't a declaration, just a normal array subscript expression.
• Eric Postpischil: Do you mean int a=2,b=3; int arr[a+b];?
• WhozCraig: It's only valid if arr is a pointer or array object declared.. somewhere. And even then, it's pointless as it doesn't actually do anything.
• Gonçalo Bastos: @Aman Sharma, you cant declare an array with local variable! The max you can do is create constats and do something like this: #define A = 2 #define B = 3 int arr[A+B];
• Eric Postpischil: @LSerni: Testing like that shows only what one specific compiler does in one specific circumstance. It does not definitively reveal what the C standard says. Such a test could pass because a compiler supports an extension not defined by the C standard, and an assignment and print could appear to work even if their behavior were undefined by the C standard. So recommending such testing is not a good way to answer questions like this.

Answer 1

An array declare with a size that is not a integer constant expression is called a variable length array. It is allowed in C, although not for arrays with static or thread storage duration.

The 1999 C standard required C implementations to support variable length arrays. The 2011 standard made support optional.

Answer 2

You can do something like this:

#include <stdio.h>
#define A 2
#define B 3
int main(){
 
 int a=A, b=B, arra[A+B];
 return 0;
}

• Gonçalo Bastos: @4386427 No but, thats the best option! I will edit it