Higher Computing

1. Higher Computing Software Development High Level Language Constructs I Power

2. What we will learn • Simple Data types • Arrays • Decision Making • Modules and Parameter Passing

3. Simple Data Types • Some of the types of variables used include: • String • Real • Integer • Boolean

4. Strings • String variables contain text and can take up a range of memory. • Two operations that can be applied are: • Concatenation. • Substrings.

5. 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”

6. 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”

7. 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.

8. 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 /

9. 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 Booleans • E.g. AND, OR, NOT.

10. Arrays • This 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

11. 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…

12. 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.

13. Decision Making (Cont.) CASE Statement CASE mark OF >= 70: Print “A” >= 60: Print “B” >= 50: Print “C” >= 45: Print “D” DEFAULT : Print “No Award” END CASE Nested IF IF 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

14. 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

15. 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.

16. Conditional Loops Do Execute this command Loop Until exit = TRUE Do While exit = FALSE Execute this command Loop

17. 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.

18. 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.

19. 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.

20. 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.

21. 5000 5001 5002 Memory Locations Passing by value (Example) The Value of the parameter stored at location 5000 is passed by value. Simon Simon Paul A copy of the value is stored at location 5001 The subroutine is then free to change the value in 5001 The value of the original remains unchanged.

22. 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.