Part 1
Arrays is a collection of elements of same type grouped under one name.
int x=10; (Here, x is a scalar variable where you can store only one element.)
int A[5]; (Here, A is a vector variable called Array.)
Declaration and Initialization
- int A[5]; Array of Size 5 is declared and it contains garbage values.
- int A[5]={2,4,6,8,10}; Initialized and declared
- int A[5]={2,4}; First and second index contain 2 and 4 whereas the rest are initialized to zero.
- int A[5]={0}; All the 5 elements are initialized to zero.
- int A[ ]={2,4,6,8,9}; Initialized and declared without specifying the size.
Traversing an Array (Using for loop)
for(i=0;i<5;i++) { printf(“%d”, A[i]); }
Printing an array
All three given below are equivalent and they print the second index element.
printf(“%d”, A[2]); Subscript
printf(“%d”, 2[A]);
printf(“%d”, *(A+2)); Pointer Arithmetic
Print Address of Array
Static vs Dynamic Array
Static Array means that the size of memory/array will be decided at compile time. Memory will be allocated only at running time. Whereas ,a dynamic array is an array with a big improvement: automatic resizing. One limitation of arrays is that they’re fixed size, meaning you need to specify the number of elements your array will hold ahead of time. A dynamic array expands as you add more elements.
Note: Size of an array can be decided at runtime in C++, but in C language it has to be mentioned at compile time ONLY. And both arrays are created in Stack as part of activation record of main function.
In the image given above, Both arrays A and B are created in Stack whereas the size of array B is declared at run time.
Now we will see how to store an Array in Heap Memory.
Note: For accessing anything from heap, we must have a pointer.
A pointer p is used to access the array A of size 5 (for now)
In any language, when you declare a variable, the memory for that variable will go inside the stack.
Heap memory cannot be accessed directly. We need memory in heap, then we need to use the malloc function in C or new function in C++.
If unused memory is not released then memory leak problem may occur.
Increasing Array Size
Let’s say you have an array of size 5 in your memory but you don’t know whether the next memory block is free or not. Therefore, you can’t increase array size directly. You have to take a bigger array instead, copy small array’s elements and then delete small array.
Here, given that size 5 of space was insufficient we made a bigger array and shifted the elements of the previous array into the bigger array of size 10.
That’s all for today. I’ll be back with part 2 where we’ll be discussing all about 2-d and 3-d Arrays.
Ciao!
