Can Array size be declared as a negative number?

What will happen if we declare Array size as a negative value?

Let us first try to declare an array size as negative. 

C++

#include <bits/stdc++.h>
using namespace std;

int main()
{
    // Declare array with negative size
    int arr[-2];
    arr[0] = -1;

    return 0;
}

Java

public class Main {
    public static void main(String[] args) {
        try {
            // Attempt to declare an array with a negative size
            int[] arr = new int[-2]; // This will throw a NegativeArraySizeException
            
            // If the array declaration succeeds, assign a value to the first element of the array
            arr[0] = -1;
        } catch (NegativeArraySizeException e) {
            // Handle the exception
            System.out.println("Cannot create an array with negative size.");
        }
    }
}

JavaScript

// Define a function that emulates the behavior of the Java Main class
function main() {
    try {
        // Attempt to declare an array with a negative size
        let arr = new Array(-2); // This will throw a RangeError
        
        // If the array declaration succeeds, assign a value to the first element of the array
        arr[0] = -1;
    } catch (e) {
        // Check if the error is due to a negative array size
        if (e instanceof RangeError) {
            // Handle the exception
            console.log("Cannot create an array with negative size.");
        } else {
            // Handle other types of errors
            console.log("An error occurred:", e);
        }
    }
}

// Call the main function
main();

Try to run the above code. You will see that this is giving an error that specifies the error is due to the negative size of the array.

Compiler error:

prog.cpp: In function ‘int main()’:
prog.cpp:7:15: error: size of array ‘arr’ is negative
     int arr[-2];
               ^

Why cannot we declare an array with a negative size?

We have seen that declaring array size gives an error. But the question is “Why”? 

As per the convention of array declaration, it is mandatory that each time an array is evaluated it shall have a size greater than 0. Declaring array size negative breaks this “shall” condition. That’s why this action gives an error.

How different Programming languages handle declaration of Array size with negative value?

Let us look at how negative size array declaration behaves in different programming languages.

In the case of Python:

Python3

from numpy import ndarray
b = ndarray((5,), int)
b = [1, 2, 3, 4, 5]
print(b)
a = ndarray((-5,), int)

Output:

[1, 2, 3, 4, 5]
Traceback (most recent call last):
  File "main.py", line 5, in <module>
    a = ndarray((-5,),int)
ValueError: negative dimensions are not allowed


** Process exited - Return Code: 1 **
Press Enter to exit terminal

In the case of C language

C

#include <stdio.h>

int main()
{
    // Declaring array with negative size
    int b[-5] = { 0 };
    printf("%d", b[0]);
    return 0;
}

Output:

./e384ec66-a75a-4a93-9af5-52e926ec600a.c: In function 'main':
./e384ec66-a75a-4a93-9af5-52e926ec600a.c:4:8: error: size of array 'b' is negative
    int b[-5]={0};
        ^

In case of C++

C++

#include <iostream>
using namespace std;
int main(){
  int arr[-5]={0};
  cout<<arr[0];
}

Output:

./72b436a2-f3be-4cfb-bf0a-b29a62704bb8.cpp: In function 'int main)':
./72b436a2-f3be-4cfb-bf0a-b29a62704bb8.cpp:4:13: error: size of array 'arr' is negative
   int arr[-5]={0};
             ^

In case of Java

Java

public class NegativeArraySizeExceptionExample {
    public static void main(String[] args)
    {
        // Declaring array with negative size
        int[] array = new int[-5];
        System.out.println(array.length);
    }
}

Output:

Exception in thread "main" java.lang.NegativeArraySizeException: -5
    at NegativeArraySizeException.mainNegativeArraySizeException.java:3)

In case of C#

C#

using System;

public class NegativeArraySizeExceptionExample{

    static public void Main (){
       // Declaring array with negative size
        int[] array = new int[-5];
        Console.Write(array.Length);
    }
}
 

Output:

prog.cs(7,32): error CS0248: Cannot create an array with a negative size

In the case of Javascript

Javascript

let arr = new Array(-5);
console.log(arr);  // This will output: [ <5 empty items> ]

Output:

x.js:1 Uncaught RangeError: Invalid array length