1. The structure of programming
F452 AS Computing

2. The basic constructs of programming
Assignment
Sequence
Selection
Iteration

3. Assignment Assigning values to variables x = 5 text1 = “Hello”
Paid = False
Integer
String
Boolean

4. Sequence
All instructions are executed once in the order in which they appear.
Instructions are done sequentially

5. Selection
There is an option of statements and a condition is used to determine which (if any) statement is executed. Eg. Using an IF statement

6. 2 Types of Selection The IF statement The ELSE part is optional.
2. The CASE statement
IF <condition> THEN
...
ELSE
END IF
SELECT CASE <variable>
CASE <value>
...
CASE <value 2>
END SELECT

7. Iteration - Loops Infinite loop Count-controlled loop
“A group of statements is executed a set number of times or until a condition is met.”
Infinite loop
Condition-controlled loop
Count-controlled loop

8. Infinite Loop 10 Print “Hello World” 20 Goto 10
Loop will never stop. No condition is coded within the loop to make it stop.
10 Print “Hello World”
20 Goto 10
Hello World

9. Condition-controlled loops WHILE loop
x=5
WHILE x > 0 Do
Begin
Print x
x = x – 1
End
END WHILE
Print “Done” 4 3 2 1
Done

10. Condition-controlled loops REPEAT UNTIL loop1 2 3 4 5 6 7 8 9 10
REPEAT
x = x + 1
Print x
UNTIL x = 10

11. Count -controlled loop1 4 9 16 25 36 49 64 81
100
FOR x = 1 TO 10
y = x * x
Print y
NEXT x

12. More about constructs
Any CASE statement can be written as a series of IF statements.
Any WHILE loop, REPEAT UNTIL loop or FOR loop can be rewritten as any of the others.
Because the condition of a WHILE loop is at the beginning of the loop, the statements in the loop may never be executed.

13. Subroutines
A subroutine is a set of statements which performs a specific task as part of a main program.
When it is defined it is given an identifier (name).
The name is used in the main program to ‘call’ the subroutine. This causes the subroutine to execute its statements before returning control to the main program.

14. Procedures Procedure Square Begin x = y * y End Main Program Begin
Procedures are subroutines which just execute their statements and return. They are usually used as instructions in the main program. They can be coded to return a value, but don’t have to.
Procedure Square
Begin
x = y * y
End
Main Program
Begin
square()
Print x
End

15. Function A sub routine or procedure that returns a value.
E.g. Sum function in Excel

16. Parameters Subroutines (functions and procedures) may have parameters.
Item of data that is given to a procedure or function
Parameters will have a data type
Parameter
Procedure PrintName (Name:String, Copies:Integer)
PrintName (solanki, 2)
Parameter

17. Arguments The values that are passed to a parameter
Procedure GetSquare (Number: Integer)
SQNumber = Number * Number
End
num:=10
GetSquare(num)
Argument

18. Recursion
Recursion is when a subroutine (a procedure or a function) calls itself. Such a subroutine is said to be recursive.
Every time the recursive subroutine is called, a new copy of the subroutine is created and executed. The copy of the subroutine which called it is suspended until the call returns.
Every recursive algorithm can be rewritten as an iterative algorithm and vice-versa.
Recursive algorithms can be easier to write and explain, but use may use memory less efficiently than the iterative version of the same algorithm.