Data Structure Arrays

Data Structure Arrays

Internally, array is a kind of data structure that can store a fixed-size sequential collection of elements of the same type. An array is used to store a collection of data, but it is often more useful to think of an array as a collection of variables of the same type.

array consists of contiguous memory locations. The lowest address corresponds to the first element and the highest address to the last element.

Arrays in C++

C++ provides a data structure, array, which stores a fixed-size sequential collection of elements of the same data-type. An array is used to store a collection of data, but it is better to think of an array as a collection of variables of the same type.

Declaration of array

int intarray[10]; // Declares an array of integer type of size 10 with elements having random values. Index ranges from 0 to 9(i.e. size-1).
int intarray[10] = { 0 }; // Declares an array of integer of size 10 with all elements having value 0

// Choose one the two declarations and then move ahead.

Inserting elements to array:

intarray[0] = 1; // Inserts an integer value of 1 at index 0
intarray[1] = 0; // Inserts an integer value of 0 at index 1
intarray[2] = -1; // Inserts an integer value of -1 at index 2
intarray[3] = 1; // Inserts an integer value of 1 at index 3

Printing an array:

std::cout << intarray[0] << std::endl; // Returns 1 which is element at index of the array
std::cout << intarray[11] << std::endl; // Would give a a "Garbage" value as there is no element at index 11 of array.
// That memory location is beyond the range of the array.

// To print all the elements of the array
for(int i = 0; i < n; i++)
	std::cout << intarray[i] << std::endl;

Basic operations on array:

std::cout << sizeof(intarray)/sizeof(intarray[0]) << std::endl; // Returns the length of the array i.e. 10.
std::cout << sizeof(intarray[0]) << std::endl; // Returns length in bytes of one array item i.e. 4 as it is an integer

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Arrays in Python

Python doesn't have a native array data structure. An array in Python should not be confused with list. The major difference between a list and an array in Python is that a list can have different types of values whereas an array should have all the values of same type.

Declaration of array

from array import array
intarray = array('i') # Declares an array of integer type

Inserting elements to array:

intarray.append(1) # Inserts an integer value of 1 to the array
intarray.append(0) # Inserts an integer value of 0 to the array
intarray.append(-1) # Inserts an integer value of -1 to the array
intarray.append(1) # Inserts an integer value of 1 to the array

intarray.append('d') # Would give a TypeError as the array is of integer type.

#Resolve the above error and then move ahead.

Printing an array:

print(intarray) # Returns array('i', [1, 4, -1])
print(intarray[0]) # Returns 1 which is the element at index 0 of the array
print(intarray[3]) # Would give IndexError as there is no element at index 3 of array.

#Resolve the above error and then move ahead.

# To print all the elements of the array
for i in intarray:
	print(i)

Basic operations on array:

len(intarray) # Returns the length of the array i.e. 3
intarray.itemsize # Returns length in bytes of one array item i.e. 4 as it is an integer
intarray.count(1) # Returns the number of occurrences of 1 in the array i.e. 2
intarray.insert(1, 3) # Insert a new item with value x in the array before position i
intarray.remove(1) # Remove the first occurrence of 1 from the array
intarray.reverse() # Reverse the order of the items in the array
intarray.pop(1) # Removes the item with the index 1 from the array and returns it

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