Programming

Concepts

Declaring

Variables and constants can be declared with a certain data type before they are assigned a value. This makes it easier to understand the purpose of a program and identify errors.

DECLARE Text : STRING
CONSTANT DaysPerWeek ← 7

Data Types

There are 5 basic data types when using pseudocode.

  • boolean
  • integer
  • real
  • char
  • string

Common Techniques

Selection

Some section of a program may require a decision to be made. These decision are often controlled by booleans. Selection allows parts of a program to be ignored depending on the value of a variable or boolean expression.

Most selection statements are done using an IF statement which runs a block of code if the condition is true.

Num ← 1
IF Num > 0 THEN
	OUTPUT "Positive"
ELSE
	OUTPUT "Not Positive"
ENDIF

    



    


  
On the other hand, a CASE statement runs a block of code when a variable is equal to value. This statement is used when it would take too many IF and ELSE statements to account for multiple cases.

  
X ← 0
Y ← 0
OUTPUT "Make your move!"
INPUT Move
CASE OF Move
	"w" : Y ← Y + 1
	"s" : Y ← Y - 1
	"d" : X ← X + 1
	"a" : X ← X - 1
	OTHERWISE OUTPUT "?"
ENDCASE
OUTPUT X
OUTPUT Y

  

    

    



    


  
Iteration

  
Repeating a process is called iteration. In programming, loops are used to perform tasks repeatedly. There are 3 types of loops.

  
  • count-controlled FOR loops
    • 
    
  • pre-condition WHILE loops
    • 
    
  • post-condition REPEAT UNTIL loops

  
🤔

  
Pre-condition loops can replace all other loops as well as selection statements.
  

  
String Handling

  
Strings are an important aspect of programming. They are similar to an array of characters (char array).

  
  • length
    • 
    
  • substring
    • 
    
  • upper
    • 
    
  • lower

  
OUTPUT LENGTH("penis")
OUTPUT UCASE("#2c6fef")
OUTPUT LCASE("X")
OUTPUT SUBSTRING("sushi", 1, 3)

  

    

    



    


  
⚠

  
The first character of a string can be at position 0 or 1 when using pseudocode. However, the first character is always at position 0 when using program code.
  

  
Operations

  
There are 3 types of operations:

  
  • Arithmetic
      
    • + (addition)
      • 
        
    • - (subtraction)
      • 
        
    • * (multiplication)
      • 
        
    • / (division)
      • 
        
    • ^ (exponentiation)
    • 
    
  • Logical
      
    • = (equal to)
      • 
        
    • <> (not equal to)
      • 
        
    • > (greater than)
      • 
        
    • < (less than)
      • 
        
    • >= (greater than or equal to)
      • 
        
    • <= (less than or equal to)
    • 
    
  • Boolean
      
    • AND
      • 
        
    • OR
      • 
        
    • NOT

  
Procedures and Functions

  
A procedure is a block of reusable code that performs a task.

  
DECLARE Items : ARRAY
PROCEDURE Swap
	Temp ← Items[Index]
	Items[Index] ← Items[Index + 1]
	Items[Index + 1] ← Temp
	Swapped ← TRUE
ENDPROCEDURE
N ← 0
Item ← ""
REPEAT
	OUTPUT "Enter an item or leave blank to begin sorting."
	INPUT Item
	IF Item <> "" THEN
		N ← N + 1
		Items[N] ← Item
	ENDIF
	Length ← N
UNTIL Item = ""
Swapped ← TRUE
WHILE N > 1 AND Swapped DO
	Swapped ← FALSE
	N ← N - 1
	FOR Index ← 1 TO N
		IF Items[Index] > Items[Index + 1] THEN
			CALL Swap
		ENDIF
	NEXT
ENDWHILE
OUTPUT Length, " items have been sorted!"
FOR Index ← 1 TO Length
	OUTPUT Items[Index]
NEXT

  

    

    



    


  
A function is similar to a procedure but it returns a value back to the main program. This makes functions very handy for calculations or recursion.

  
FUNCTION SumUpTo(Value)
	RETURN Value / 2 * (Value + 1)
ENDFUNCTION
OUTPUT SumUpTo(4)

  

    

    



    


  
Library Routines

  
Library routines are pre-written functions in pseudocode that are used to perform common tasks. Programming languages tend to collectively call this a standard library.

  
  • MOD
      
    • returns the remainder after a division operation
    • 
    
  • DIV
      
    • returns the floor of a division operation (performs integer division and rounds the result down)
    • 
    
  • ROUND
      
    • rounds a number to the nearest integer
    • 
    
  • RANDOM
      
    • returns a random decimal number between 0 and 1

  
Maintainable Program Standards

  
Good programmers create maintainable programs. A maintanable program includes the appropriate use of:

  
  • meaningful identifiers (to allow programmers to easily understand the purpose of a variable)
    • 
    
  • the commenting feature provided by the programming language (to help programmers know the purpose of a section of code)
    • 
    
  • procedures and functions (to make programs modular and easy to update)
    • 
    
  • relevant appropriate commenting of syntax

  
A meaningful identifier exlpains the purpose of a variable. For example, a variable used to store a running total should have a name like Total or Sum.

  
🤔

  
It is usually a good idea to use verbs as identifiers for functions and procedures.
  

  
Arrays

  
Arrays are fixed-length structures containing elements with the same data type which are accessible by consecutive index numbers. It is good practice to explicitly state what the lower bound of the array (the index of the first element) because this defaults to either 0 or 1 in different systems. Generally, a lower bound of 1 will be used in pseudocode.

  
DECLARE TicTacToe : ARRAY[1:3, 1:3] OF CHAR

  


  
File Handling

  
Storing data in files permanently allows data to be resued by a program even after it has been closed and reopened. Files also allow data to be transferred between machines.

  
The pseudocode below shows the process of writing the text stored in FileA.txt to FileB.txt. This will replace the existing contents of FileB.txt but leave FileA.txt unmodified.

  
DECLARE LineOfText : STRING
OPENFILE FileA.txt FOR READ
OPENFILE FileB.txt FOR WRITE
READFILE FileA.txt, LineOfText
WRITEFILE FileB.txt, LineOfText
CLOSEFILE FileA.txt
CLOSEFILE FileB.txt

  

    

    



    





        
Deez Nuts!