constants & variables

Constants & Variables

What are they?

Constant: a value that never changes

Variable: a value that can be changed

To get an idea of how a computer works with values, we need to know a bit about Memory...


MemoryWe can imagine a computer's memory like a kind of electronic storage cabinet:-


Memory AddressesEach drawer has a number, like houses on a street Allows the computer to access data like DHL does with parcels

Lets the computer keep track of where, not what

Too fiddly & complicated to be useful to humans


Variables Like labels on the drawers

Lets us (our program) keep track of what not where

We don't need to know anything about memory addresses!


More About Variables

Like storage cabinet drawers: we can put values in (write)

Unlike drawers: variables can only store one value at a time

when we take values out (read) the value stays there

Variables are so-called because they are Read/Write their values can be changed they're variable!


Constants Value fixed when program is written

Stored in memory like variables but are Read Only

Their value is never changed - they're constant!

In programs we put constant names in UPPER CASE

Examples: DAYS_IN_WEEK = 7

ML_PER_TEASPOON = 4.9289216

UK_CAPITAL = London


Using Constants & Variables

Time to play! Start the IDLE software:


Introducing the Print command

The print command prints what's between ' and 'Try using your name:

It also prints sums for you. Try it:


Now let's try some text variables (also called strings):

And some numbers:


More fun with variables:

Notice how the commas are used to separate the variables from each other.

Some more sums

Notice how Python uses * for and / for


Summary

Constants & Variables are labels for values stored in a computer's memory by a program

Constants are fixed when a program is written used to store values which never change

Variables can be changed by the program when it is running they can contain numbers or text

constants & variables

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