Introduction

Pseudo code (or Structured English) is used to specify program logic in a (somewhat) English like manner, that aims to be independent of any particular programming language. This simplifies program development by separating it into two main parts, logic design and coding. The use of pseudo code allows the programmer to focus on the logic of the program rather than implementation details such as how data is displayed Once the logic is developed, coding becomes the translation of the pseudo code into the required programming language.

Sequence

Assignment

Format

variable = expression

Examples

total = 0
y = x * x + z / 4 - 1
name = "Joan Smith"
validLength = True

Input

Format

Input variable, variable, ...

Examples

Input custName
Input distance, speed

Display

Format

Display value, value, ...

Examples

Display "Hello World"
Display totalPrice, taxPayable
Display "Customer Number: ", custNum, "Name: ", custName

Selection

If-Else

Format

IF condition THEN
   statement
   statement
   ...
ENDIF
 

IF condition THEN
   statement
   statement
   ...
ELSE
   statement
   statement
   ...
ENDIF
 

IF condition THEN
   statements
ELSE
   IF condition THEN
       statements
   ELSE
       IF condition THEN
           statements
       ELSE
          statements
       ENDIF
   ENDIF
ENDIF
 

IF condition THEN
   statements
ELSE IF condition THEN
   statements
ELSE IF condition THEN
   statements
ELSE
   statements
ENDIF

Note: the Else part is optional. Use it where required by the logic.

Examples

IF lineNumber > 50 THEN
   Display ""
   Display "Student Number", "Student Name"
   lineNumber = 0
ENDIF
 

IF monthNumber >= 1 AND monthNumber <= 12 THEN
   Display "valid month"
ELSE
   Display "invalid month"
   Display "Month must be between 1 and 12"
ENDIF
 

IF mark >= 80 THEN
   grade = "A"
   comment = "Excellent"
ELSE
   IF mark >= 70 THEN
       grade = "B"
   ELSE
       IF mark >= 60 THEN
           grade = "C"
       ELSE
           IF mark >= 50 THEN
               grade = "D"
           ELSE
               grade = "N"
               comment = "Poor"
           ENDIF
       ENDIF
   ENDIF
ENDIF
 

IF mark >= 80 THEN
   grade = "A"
   comment = "Excellent"
ELSE IF mark >= 70 THEN
   grade = "B"
ELSE IF mark >= 60 THEN
   grade = "C"
ELSE IF mark >= 50 THEN
   grade = "D"
ELSE
   grade = "N"
   comment = "Poor"
ENDIF

Iteration (Repetition)

For

Format

FOR counter = start-value to end-value DO
   statement
   statement
   ...
ENDFOR

Example

FOR x = 1 to 10 DO
   xSquared = x * x
   Display x, xSquared
ENDFOR

While

Format

WHILE condition DO
   statement
   statement
   ...
ENDWHILE

Example

count = 1
WHILE count <= 10 DO
   Display count
   Add 1 to count
ENDWHILE

Programs

Format

program-name()
   statement
   statement
   ...
STOP

Example

addTwoNumbers()
   Input number1, number2
   sum = number1 + number2
   Display sum
STOP 

Subprograms: Subroutines and Functions

Subroutines

Subroutines are also called procedures or void methods. Subroutines do not return a value.

Format - subroutine calls

subroutine-name()
subroutine-name(parameter, parameter, ...)

Examples - subroutine calls in a program

demoProgram()
    ...
   displayTenStars()
   displayAverage(count, total)
STOP

Format - subroutine declarations

subroutine-name()
   statement
   statement
   ...
EXIT

subroutine-name(parameter, parameter, ...)
   statement
   statement
   ...
EXIT

Examples - subroutine declarations

displayTenStars()
   FOR numStars = 1 to 10 DO
       Display "*"
   ENDFOR
   Display ""
EXIT

displayAverage(count, total)
   IF count > 0 THEN
       average = total / count
       Display average
   ELSE
       Display "Error, nothing to average"
   ENDIF
EXIT

Functions

Functions are also called non-void methods. Functions return a single value.

Format - function calls

function-name()
function-name(parameter, parameter, ...)

Examples - function calls in a program

demoProgram()
    ...
   month = inputMonth()
   IF oddNumber(month) THEN
       ...
   ENDIF
   volume = 4 /3 * PI * cube(radius)
   max = maximumNumber(a, b)
STOP

Format - function declarations

The following are called functions. They return a single value.

function-name()
   statement
   statement
   ...
RETURN with value

function-name(parameter, parameter, ...)
   statement
   statement
   ...
RETURN with value

Examples - function declarations

inputMonth()
   Input monthNumber
   WHILE monthNumber < 1 OR monthNumber > 12 DO
       Display "Error invalid month number"
       Input monthNumber
   ENDWHILE
RETURN with monthNumber

oddNumber(num)
   oddNumber = false
   IF num modulus 2 = 0 THEN
       oddNumber = true
   ENDIF
RETURN with oddNumber

cube(number)
   cube = number * number * number
RETURN with cube

maximumNumber (number1, number2)
   IF number1 >= number2 THEN
       maximumNumber = number1
   ELSE
       maximumNumber = number2
   ENDIF
RETURN with maximumNumber

Keywords

The following words have a special meaning in Pseudo Code (in this subject) and should only be used for the purposes described above.

AND, DO, ELSE, ENDIF, ENDFOR, ENDWHILE, EXIT, FOR, IF, NOT, OR, RETURN, STOP, THEN, TO, WHILE.

Other statements: Display, Input
Operators:  =, +, -, *, /, (), <, <=, >, >=, []

 

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