课 16, 主题 1

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Fundamental Components Of Programs Edexcel

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Exam code:1CP2

Constants, Variables, Initialisation & Assignment

Constants

A constant is an identifier set once in the lifetime of a program
Constants are named in all uppercase characters
Constants aid the readability and maintainability
If a constant needs to be changed, it should only need to be altered in one place in the whole program

Python examples
`PI = 3.142`
`VAT = 0.20`
`PASSWORD = "letmein"`

Variables

A variable is an identifier that can change in the lifetime of a program
Variables are named in lowercase characters unless combining multiple words
A variable can be associated a datatype when it is declared
When a variable is declared, memory is allocated based on the data type indicated

Python examples
`score = int()` # whole number
`cost = float()` # decimal number
`light = bool()` # data can only have one or two values

Initialisation & assignment

A variable can be initialised with a value
The assignment operator = is used to set or change the value of a variable

Python examples
`score = 10` # Initialise with a value
`cost = 9.50` # Initialise with a value
`count = count + 1` # Adds one to the current value of count

Inputs & Outputs

Inputs

The input() function is used to capture an input from the user
All inputs default to strings and may need converting to the required data type in the program

Python examples
`surname = input("Enter your surname: ")`
`examScore = int(input("Enter your exam score: "))`
`height = float(input("Enter height: "))`

Outputs

The print() function is used to output to the screen

Python examples

print("Hello world")

examScore = 90

print(examScore)

print("Exam score: ", examScore)

An output can be formatted to the users needs using string formatting {}

Python examples
`print("{:.2f}".format (price))` # Displays a currency value to two decimal places
`print(f"Pi approximation: {pi_approx}")` # Displays a variable formatted as a string with a label

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