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Understand the scope of variables
Understand the terms 'modular' and 'subprogram'
Understand the terms parameter and parameter passing
Program code often gets very messy unless it is broken up. A program can be broken into chunks to make the program more modular.
Programs are often made up of chunks of code that performs different tasks that are repeated throughout the program.
These chunks of code are called subprograms.
Each subprogram is given a unique name so that it can be referenced later on without having to rewrite the code each time it is used.
Often called subroutines, procedures, methods and functions, a subprogram is a clear and independent piece of code that performs a certain task.
We have been looking at predefined functions which are in fact themselves subprograms built in to the programming language.
These predefined functions, such as round will perform a specific job and nothing more.
We too can define our own subprograms.
When we need to run the code within a subprogram, we call it.
The subprogram receives data from the program and performs an action on it (for example, you might expect the printDoubleNumber subprogram to print a number multiplied by 2)
To call it, we use its name followed by brackets and any parameters we need to pass to it, take for example a subprogram called doubleNumber, we could call it using the parameter 2 by using:
printDoubleNumber(2)def printDoubleNumber(num):
print(num * 2)
printDoubleNumber(2)A subprogram definition
A call to a subprogram
A function is like a mathematical function, it takes in a value and then performs a process on it and gives it back as an output.
In general, a function is a subprogram that can give back a value. It uses the return keyword to instruct the program to send the data back:
def printDoubleNumber(num):
return num * 2
x = 10
y = printDoubleNumber(x)
print(y)x = 10
printSquareNumber(x)
def printDoubleNumber(num):
print(num * 2)
def printAverage(name, mark1, mark2):
average = (mark1 + mark2) / 2
print("Pupil", name, " got an average of", average)
printAverage(21, 34, "John")Identify which of the following programs have formal parameters and which have actual parameters:
def squareIt(num):
def displayOnScreen(num):
1.
2.
print(y)3.
print(x * 2)4.
def addNumber(n):
print(x + n)
def setX():
x = 10
setX()
addNumber(5)function changeX(&$x){
$x = 20;
}
$x = 10;
echo $x;
changeX($x);
echo $x;def printIt(z):
global y
x = 20
print(x, y, z)
y = 10
printIt(5)
Local variable
Global variable
Note the importance of line 2 which contains this 'global' word. This tells Python that whenever it references the variable y (e.g. setting the value or getting the value), use the global version of it
In your own words, explain the difference between passing by reference and passing by value.
Open Python IDLE, create a subprogram which returns a number multiplied by 3. Your program should include a global variable which contains the number 3 and some local variables.
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