2.2 Programming Fundamentals

Variable - A variable is a value stored in memory that can change while the program is running.

CAsting - Converting data types This process is known as casting. The following examples convert a string to an integer and an integer to a string: str(68) returns “68” int(“54”) returns 54 float(“5.4”) returns 5.4

Each data type is allocated a different amount of memory Integer - A positive or negative whole number used when arithmetic will be required Real / Float - A positive or negative decimal number Character - A single alphanumeric String - Multiple characters joined together [n.b. use this for credit card numbers] Boolean - two inputs(true and false)

word = “Hello World” length = len(word) = 10 • *word[0:3]** = “Hel” • *word[-3:] = “rld”** • *print word[3:] = “lo World”** • *print word[:-3] #get all but the three last character​** • *word.upper() = “HELLO WORLD”** • *word.lower() = “hello world”**

Constant - A value which remains fixed as does not change whilst the program is running. It must be set at design time when the program is first written.

Sequence is executing one instruction after another

Selection is program branching depending on a condition.

Iteration, sometimes called looping, is repeating sections of code.

It allow Sub-programs to recieve data in the format they were expecting.

• Open the file for creating/overwriting or appending to a file My • Write the data to a file • Close the file

• Open the file for reading data • Assign a boolean variable to “false” to indicate the end of file is not reached. • While the end of the file is false and the search item is not found: • Read data from the file • If the data matches what is being searched for, assign the data to variables or output. • Check if the end of the file has been reached and assign the Boolean variable to “true” • Close the file

Data in data bases are stored as records. Each records contains a number of fields and each field has its own data type

A record structure: • A collection of related fields • Each field is a variable • Each field in a record can have a different data type.

• Stored on the secondary storage • Used to store data when the application is closed. • Useful for small volumes of data. E.g. configuration files. • Each entry is stored on a new line or separated with an identifier such as a comma or tab. • Can require a linear search to find/read data which is slow (if there is no order to the data or record structure). • Structured text files E.g. CSV, XML & JSON are popular for storing and exchanging data between applications

• Stored in RAM. • Used to store data when a program is running. • Useful for small volumes of data an algorithm is using. • Can be single or multi-dimensional allowing for tables of data to be stored. • Uses indexes to refer to data items. • Efficient algorithms or linear searches can be used to find data

• Often stored on remote servers. • Often used to store data shared by many users, e.g. ticket booking system. • Data is stored in records and fields. • Uses advanced data structures to store data efficiently. • Uses very efficient algorithms to search and sort data executed on the servers. • More secure than text files. • The order of the fields in the database in independent of the code

There are three commands you need to know: SQL is used to create, delete, modify and manipulate records in a database The basic commands include: • SELECT which fields to be returned. * can be used to indicate all fields. • *- FROM which table. Databases can have more than one table, each with their own unique name.** • WHERE records meet a condition. Like can be used as a wildcard.

An array is a series of memory locations – each of which holds a single item of data, but with each location sharing the same name. All data in an array must be of the same data type We can do that by allocating a contiguous part of memory to storing that data. Our program will know where in memory out array starts. It uses a index relative to this start point to allow us to easily access the arrays contents.

You can visualise a two dimensional array as looking like a table with two sets of indexes. One index for the rows, another for the columns. print(countries[0][0]) creates “Angola” and 1246700

Procedures • Carry out a task & DO NOT RETURN A VALUE • Provide structure to code making it easier to read Functions • Carry out a task AND Return a value • Create reusable program components