I Power

Higher Computing

Software Development

High Level Language Constructs

What we will learn

Simple Data types

Arrays

Decision Making

Modules and Parameter Passing

Simple Data Types

Some of the types of variables used include:String

Real

Integer

Boolean

Strings

String variables contain text and can take up a range of memory.

Two operations that can be applied are:Concatenation.

Substrings.

Concatenation

Concatenation is the addition of two strings.

One string is placed at the end of the other.Forename$ = “Bob”

Surname$= “Jones”

Fullname$ = Forename$ + Surname$

The Variable Fullname$ will now contain:

“BobJones”

Substrings

Substrings are often referred to as string slicing.This is where the part of the string is extracted.

A Variable Fullname$ may contain:

“BobJones”

Forename$ := Fullname$(1:3)

Surname$ := Fullname$(4:8)

Forename$ now contains “Bob” and

Surname$ now contains “Jones”

Real

Real numbers are floating point numbers.

They usually use 32 bits of computer memory in a single memory location.

Remember:E.g. 20.125 = .20125 x 100 = .20125 x102

Any number can be represented in the form:

M x basee

Where M is the mantissa and e is the exponent.

Integer

An Integer is any positive or negative whole number.

Integers usually use 32bits of computer memory.

All mathematical operations can be applied to these numbers.

E.g. + - x /

Boolean

A Boolean value can have either the value True or False.

Their value is stored using one bit of memory.

Logical operators can be used on BooleansE.g. AND, OR, NOT.

ArraysThis is a set of data items of the same type grouped together with a single variable name.Each Data item (Element) in the array is identified by the variable name and a subscript (index).

An array of names may look like this:

Name(1) Contains John

Name(2) Contains Helen

Name(2) Contains Peter

Decision Making

All languages have some decision-making construct.

IF, where the execution of an action depends on a stated condition.

Most languages expand this to allow for a series of outcomes using:

IF…THEN…ELSE…

Decision Making (Cont.)

The IF…THEN…ELSE… construct can be replaced with a CASE (SWITCH) statement.

The CASE statement is no different once translated to machine code.

The advantage is that it is clearer to read and understand.

Decision Making (Cont.)Nested IFIF mark >= 70 then

PRINT “A”ELSE IF mark >= 60 then

PRINT “B”ELSE IF mark >= 50 then

PRINT “C”ELSE IF mark >= 45 then

PRINT “D”ELSE

PRINT “No Award”END IF

CASE StatementCASE mark OF

>= 70: Print “A”>= 60: Print “B”>= 50: Print “C”>= 45: Print “D”DEFAULT : Print “No

Award”END CASE

Fixed Loops

A For loop can be used to execute one or more commands a known amount of times.For counter = 1 to total

execute this command

Next

Conditional Loops

A Conditional Loop can be used when the programmer does not know how many times the code will have to be repeated.

The test to loop again can be done at the start or at the end.

Conditional Loops

Do

Execute this command

Loop Until exit = TRUE

Do While exit = FALSE

Execute this command

Loop

Modules

Well written code is often broken down into several modules

This allows different programmers to each write a separate part of the solution.

This also means that should you wish to change part of your code during the maintenance phase, the affected part can be lifted out and replaced without affecting the rest of the code.

Modules (Cont.)

Modules can take many different form depending on the language.

The two main modules we need to know about are:

Subroutines (Procedures); This is a section of code designed to do a specific task. They are then called during the running of the code.

Functions; This is similar to a subroutine except that it has a value that can be assigned rather than returning a variable.

Scope

The parts of the program that can see and use the variable are called the scope of the variable.

Local variables exist only within a single module and cannot be accessed from elsewhere in the code.

Global variables are created in the main part of the program and can be seen from any part of the program.

Parameter passing by value(In Parameter)

When a parameter is passed by value into a subroutine an exact copy of current value of the original variable is used by the subroutine.

This allows one-way data transfer between the main program and the subroutine.

The programmer can then guarantee that the variable will still be suitable for other parts of the code.

Passing by value (Example)The Value of the parameter stored at

location 5000 is passed by value.

Memory Locations

500050015002

A copy of the value is stored at location 5001

Simon

The subroutine is then free to change the value in 5001

The value of the original remains unchanged.

SimonPaul

Parameter Passing by Reference(In/Out Parameter)

Parameter passing by reference allows the data that is passed into a subroutine to be changed, then passed back out to other parts of the program.

This allows a two way data transfer between the main program and the subroutine.