arrays

1-D array:
---------
	A pointer that points to 0th element of the array and a pointer that points to whole array are totally different.
	
		Ex : int arr[5] = {1,2,3,4,5}; 
	    
		     int *ptr1 = arr;
	  
		    int (*ptr2[5]) = arr;

		when we perform increment on ptr1 and ptr2, we get different addresses like 1004 and 1020.

2-D array:
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	An array of 1-D array is known as "2-D array".

	It is also known as matrix.

	Matrix is a table of rows and columns.

	Ex : int arr[2][3]; => 2 rows and 3 columns

	Initialisation of 2-D array :
	----------------------------
		There are 2 ways to initialise 2-D array during declaration:

		1. int arr[2][3] = { {1,2,3},
				     {4,5,6} };

		2. int arr[2][3] = {1,2,3,4,5,6};

	Size of array is : 
			rows * columns * sizeof(array_type)	
	
	When we initialise a 1-D array during declaration we can skip the size of it,
	
	but with 2-D array we need to always specify the 2nd dimension(columns).

	Ex :
	   int arr[]     = {1,2,3,4,5};  // valid

	   int arr[2][2] = {1,2,3,4};   //valid

	   int arr[][2]  = {1,2,3,4};   //valid

	   int arr[2][]  = {1,2,3,4};   //Invalid

	   int arr[][]   = {1,2,3,4};   //Invalid

		NOTE : To check warnings and errors for above 

			gcc array.c -o array -Wall


	To access 2nd element of 1st row in array compiler will calculate 
	
			offset = 1 * column_no + 2	

	Dereferncing  a pointer to array gives the base address of the array.

		*(arr+i) : points to the base address of the ith 1_d array.
	
	NOTE: 
		The address of arr+i ,*(arr+i) is same, but the base type is different.
	
		base type of arr+i is pointer to 2 integers.
		
		int (*ptr)[2];
	
		base type of *(arr+i) is pointer to integer.
		
		int *ptr;

		To access individual elements of 2-D array we use *(*(arr+i)+j).
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