Data Types & Structures

Data Types

Data types are important when programming. The computer has to know whether to expect numbers, text, or other types of values. We studied a little about how data is stored during the computer systems topic.

In Python

Giving a set Value

# This is an integer

myage = 15

# This is a real(float) number

price = 0.99

# This is a string

faveSubject = "Computing"

# This is a character (Python does not have a dedicated character data type, so characters are stored as strings of length 1.)

firstInitial = "F"

# This is a Boolean

isStudent = True

Input from User

# When you input a string...

name = input("Please enter your name")

# When you input an integer number, use int( )

age = int(input("Enter age"))

# When you input a real number, use float( )

price = float(input("Enter price"))

Data Structures - 1D Array

The 1-D array data structure is used in a program to store a collection of data objects of the same type.

Let’s say we have a program that asks for 3 test scores, adds them together, and prints out the total.

It could probably start with something like this:

score1 = int(input("Please enter first score"))

score2 = int(input("Please enter second score"))

score3 = int(input("Please enter third score"))

What happens when we need a program that asks for 20 scores? Or 100? We could write out every variable, but it would be a very long program, and the chance for mistakes is high. Instead, we need a list...

This is called an array. Where a normal variable stores data in one memory location, an array reserves a whole set of memory locations, one after the other. You can think of an array like a list:

An array is like a variable that stores multiple values. We start counting the elements from 0 (instead of 1).

So element 0 in that array is 15, element 1 is 20, and element 7 is 19.

Like variables, arrays have data types (a string array, an integer array, a Boolean array, etc.)

When you see the term data structure, this refers to a variable or an array.

In Python

Declaring the Array

# An array of five empty strings

pupilnames = [str]*5

# An array of five integers, all set to 0

scores = [int]*5

# An array of ten real numbers

prices = [0.0]*10

With Pre-set Values

# An array of nine scores out of 20

scores = [15, 20, 19, 18, 17, 20, 16, 19, 12]

Using Elements in the Array

# Get the fourth element from the array

iwant = scores[3]

We know that arrays are used for a list of data, to reduce repetition (having separate variables for score1, score2, all the way to score100…) Likewise, we know that loops are used to cut down on repetition in our lines of code.

We can use a loop to traverse the array - that means, to travel through it, or loop through it.

Printing an Array

# An array of seven names

names = [“Dopey”, “Grumpy”, “Doc”, “Bashful”, “Sneezy”, “Sleepy”, “Happy”]

# The array elements are numbered from 0 to 6

# Loop from 0 to 6 and print the name

for counter in range(0, 7):

print(names[counter])

Populating an Array

names = [str] *20

scores = [int] *20

for counter in range(0,20):

names[counter] = input("Enter the name: ")

scores[counter] = int(input("Enter their score: "))

print(names)

print(scores)

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