ICAPRG301A Week 2 Strings and things Charles Babbage Developed the design for the first computer which he called a difference engine, though he never built it. This has now been built based upon his design. He also worked on a more advanced model called the Analytical Engine with another computing pioneer Ada Lovelace. However the design was never completed. On two occasions I have been asked [by members of Parliament]: 'Pray, Mr. Babbage, if you put into the machine wrong figures, will the right answers come out?' I am not able rightly to apprehend the kind of confusion of ideas that could provoke such a question - Charles Babbage ICAPRG301A Apply introductory programming techniques

ICAPRG301A Week 2Strings and things ICAPRG301A Apply introductory programming techniques Variables Read the notes carefully Variable are words used in a program to stand for data Useful when we don’t know the exact data or it will change Can be various types of numbers (Integer, Float etc), words (called Strings), booleans (True or False) etc Variable have scope, which means they exist in certain places In Python variables only exist once they have been given a value

ICAPRG301A Week 2Strings and things ICAPRG301A Apply introductory programming techniques Variables types Numbers (Integers, Decimals, Money, Time, Binary) In Python we have int and float as the main number variables Text (Strings, characters) In Python we mainly use Strings Boolean (True or False) In Python we use the key words True, False. It also has a key word None which is used to show a variable is empty ArrayIn Python we use List as the major array, but there is also Dictionary, Set List Comprehension, Generator etc There are 10 types of people, those who understand binary, and those who don’t

ICAPRG301A Week 2Strings and things ICAPRG301A Apply introductory programming techniques Variables assignment a = 5 in Python this sets the variable a to the value of 5 b = a in Python this sets the variable b to the value of 5 b= b + 5 in Python this is worked out by first calculating the right hand side and then assigning it to the left hand side c = d + bin Python this will throw an error because the variable d does not yet have a value In all these examples a single equal sign means assignment. A computer is a literal beast: it will do exactly what it thinks you told it to do. Unfortunately, that is not necessarily what you think you told it to do.

ICAPRG301A Week 2Strings and things ICAPRG301A Apply introductory programming techniques Variables scope a= 5 def double(x): a = x + x double (a) print (a) Consider this code what will it print? 1.a Throw an error

ICAPRG301A Week 2Strings and things ICAPRG301A Apply introductory programming techniques Lists Special type of variable, called Arrays in some languages Each list contain elements, these elements can be ordinary variables or other lists Declared like any variable but list is surrounded by [] and elements separated by, eg list = [1,’hello’, [‘a’,’b’,’c’], True] Accessed by using slicing

ICAPRG301A Week 2Strings and things ICAPRG301A Apply introductory programming techniques Functions Sometimes called methods or procedures Small bits of code that can be named and used as a single command Basic building blocks of programming In a well constructed program everything is inside a function In Python is defined by the command def