# A-level Computing 2009/AQA/Problem Solving, Programming, Data Representation and Practical Exercise/Problem Solving/Pseudo code

Pseudocode uses a combination of programming terminology and plain English to describe algorithms in a form that is easier for people to understand than conventional programming language code. There are no standards for pseudocode and a program in pseudocode is not an executable program. Psuedocode is used in textbooks and scientific publications to describe various algorithms, and also in planning of computer program development, for sketching out the structure of the program before the actual coding takes place. It typically leaves out details that are not essential for human understanding of the algorithm, such as variable declarations, system-specific code and some subroutines.
* Example: Pseudocode
* Below is an example of a pseudocode algorithm
* For i ← 1 to 100
* output_number ← true
* if i mod 3 equals 0
* output "Bizz"
* print_number ← false
* if i mod 5 equals 0
* output "Buzz"
* print_number ← false
* if print_number equals true
* output i
* output newline
* Converting this into VB.NET, we get:
* dim print_number as boolean
* For i = 1 to 100
* print_number = true
* if i mod 3 = 0 then
* console.writeline("Bizz")
* print_number = false
* end if
* if i mod 5 = 0 then
* console.writeline("Buzz")
* print_number = false
* end if
* if print_number then
* console.writeline(i)
* end if
* console.writeline

## Structured English

Structured English is very similar to Pseudo code, but it tends not to use so many mathematical symbols. Often people start with Structured English, convert it to Pseudo Code and then write Executable Code. Examples of common keywords: START, BEGIN, END, STOP, DO, WHILE, DO WHILE, FOR, UNTIL, DO UNTIL, REPEAT, END WHILE, END UNTIL, END REPEAT, IF THEN, IF, ELSE, IF ELSE, END IF, THEN, ELSE THEN, ELSE IF, SO, CASE, EQUAL, LT, LE, GT, GE, NOT, TRUE, FALSE, AND, OR, XOR, GET, WRITE, PUT, UPDATE, CLOSE, OPEN, CREATE, DELETE, EXIT, FILE, READ, EOF, EOT, WITH, RETURN
| Structured English | Pseudo Code | Executable Code |
| BEGIN READ name IF name EQUAL "Harry" THEN WRITE "Why don't you marry Pippa?" ELSE WRITE "Are you Royal enough?" END IF END | BEGIN INPUT name IF name == "Harry" THEN OUTPUT "Why don't you marry Pippa?" ELSE OUTPUT "Are you Royal enough?" END IF END | dim name as string name = console.readline if name = "Harry" then console.writeline("Why don't you marry Pippa?") else console.writeline("Are you Royal enough?") End if |
* Exercise: Pseudocode
* What are the rules when writing pseudocode?
* Answer:
* There are no set rules, but the code should provide clear descriptions of the algorithms being outlined.
* What is the difference between pseudocode and a programming language such as javascript?
* Answer:
* Pseudocode cannot create executable code, whilst javascript can.
* For the following pseudocode write a VB.NET equivalent:
* for x from 1 to 7 inclusive
* add x to total
* loop
* print total
* Answer:
* dim total as integer = 0
* for x = 1 to 7
* total = total + x
* next
* console.writeline(total)
* Write pseudocode for the following problem:
* Find the average of 4 numbers and display it
* Answer:
* There are many ways to answer this correctly as long as it is clear you got it right. Ask your friend to check it.
* input 4 numbers
* sum = add numbers together
* avg = sum / 4
* print avg