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As you will probably know the name of the array identifies the address of its first element. When you try to compile a program that uses an array with a negative index the compiler will not warn you about anything because it is a legal operation. Example: {{{ array[2] //its the same of saying take the address array and sum 2 to the address and then take the value in that portion of memory *(array+2) array[-2] //its the same of saying take the address array and subtract 2 to the address and then take the value in that portion of memory *(array-2) }}} Now the problem is that when you do something like {{{int array[10];}} You allocate the space only for 10 slots of memory addresses after the array start position in memory. This means that array[0], array[1], array[2], ... array[9] are safe but there is no guarantee for array[10], array[11], ... or array[-1], array[-2] etc.... However when creating arrays using pointers this is possible to do if you know exactly that at array[-2] there is valid data that you need to use. - Giovanni Murru July 17, 2014 | Flag Reply

In C and C++ yes, it is allowed.
In java you will get 'ArrayIndexOutOfBoundsException'.
You can easily mess around with addresses in C. That is both the beauty and the drawback of using C language.

Now try predicting the output of this question:

#include<stdio.h>
int main()
{
	int a[3],i;
	for(i=-1;i<3;i++)
	{
//		printf("i is %d\n",i);
		a[i]=-2;
//		printf("i is %d\n",i);
	}
}

This gives you an infinite loop because a[-1] points to i
a[i]=-2 means i=-2.
Then i++ changes i to -1
and it gets stuck in an infinite loop!

Due to these security issues is C, there came the arrival of a new programming language- Java, which is nothing but modified C++ to remove security vulnerabilities and have better checks for overflows,etc.

- neerajlakhotia08 July 17, 2014 | Flag Reply

In C,it does not give any compilation error but we cant print the array value for that particular index,as it hangs the compiler during run time.

- rex.rishabh801 July 21, 2014 | Flag Reply

But why a[-1] points to i??

- Anonymous August 02, 2014 | Flag Reply