Pseudocode is a kind of structured english for describing algorithms. It allows the designer to focus on the logic of the algorithm without being distracted by details of language syntax. At the same time, the pseudocode needs to be complete. It describe the entire logic of the algorithm so that implementation becomes a rote mechanical task of translating line by line into source code.PSEUDOCODE STANDARD
In general the vocabulary used in the pseudocode should be the vocabulary of the problem domain, not of the implementation domain. The pseudocode is a narrative for someone who knows the requirements (problem domain) and is trying to learn how the solution is organized. E.g.,
Extract the next word from the line (good)Note that the logic must be decomposed to the level of a single loop or decision. Thus "Search the list and find the customer with highest balance" is too vague because it takes a loop AND a nested decision to implement it. It's okay to use "Find" or "Lookup" if there's a predefined function for it such as
set word to get next token (poor)Append the file extension to the name (good)
name = name + extension (poor)
FOR all the characters in the name (good)
FOR character = first to last (ok)
String.indexOf().
Each textbook and each individual designer may have their own personal style of pseudocode. Pseudocode is not a rigorous notation, since it is read by other people, not by the computer. There is no universal "standard" for the industry, but for instructional purposes it is helpful if we all follow a similar style. The format below is recommended for expressing your solutions in our class.
The "structured" part of pseudocode is a notation for representing six specific structured programming constructs: SEQUENCE, WHILE, IF-THEN-ELSE, REPEAT-UNTIL, FOR, and CASE. Each of these constructs can be embedded inside any other construct. These constructs represent the logic, or flow of control in an algorithm.
It has been proven that three basic constructs for flow of control are sufficient to implement any "proper" algorithm.
SEQUENCE is a linear progression where one task is performed sequentially after another.
WHILE is a loop (repetition) with a simple conditional test at its beginning.
IF-THEN-ELSE is a decision (selection) in which a choice is made between two alternative courses of action.
Although these constructs are sufficient, it is often useful to include three more constructs:
REPEAT-UNTIL is a loop with a simple conditional test at the bottom.SEQUENCE
CASE is a multiway branch (decision) based on the value of an expression. CASE is a generalization of IF-THEN-ELSE.
FOR is a "counting" loop.
Sequential control is indicated by writing one action after another, each action on a line by itself, and all actions aligned with the same indent. The actions are performed in the sequence (top to bottom) that they are written.
Example (non-computer)
Brush teethExample
Wash face
Comb hair
Smile in mirror
READ height of rectangleCommon Action Keywords
READ width of rectangle
COMPUTE area as height times width
Several keywords are often used to indicate common input, output, and processing operations.IF-THEN-ELSE
Input: READ, OBTAIN, GET
Output: PRINT, DISPLAY, SHOW
Compute: COMPUTE, CALCULATE, DETERMINE
Initialize: SET, INIT
Add one: INCREMENT, BUMP
Binary choice on a given Boolean condition is indicated by the use of four keywords: IF, THEN, ELSE, and ENDIF. The general form is:
IF condition THENThe ELSE keyword and "sequence 2" are optional. If the condition is true, sequence 1 is performed, otherwise sequence 2 is performed.
sequence 1ELSE
sequence 2ENDIF
Example
IF HoursWorked > NormalMax THENWHILE
Display overtime messageELSE
Display regular time messageENDIF
The WHILE construct is used to specify a loop with a test at the top. The beginning and ending of the loop are indicated by two keywords WHILE and ENDWHILE. The general form is:
WHILE conditionThe loop is entered only if the condition is true. The "sequence" is performed for each iteration. At the conclusion of each iteration, the condition is evaluated and the loop continues as long as the condition is true.
sequenceENDWHILE
Example
WHILE Population < Limit
Compute Population as Population + Births - DeathsENDWHILE
Example
WHILE employee.type NOT EQUAL manager AND personCount < numEmployeesCASE
INCREMENT personCountENDWHILE
CALL employeeList.getPerson with personCount RETURNING employee
A CASE construct indicates a multiway branch based on conditions that are mutually exclusive. Four keywords, CASE, OF, OTHERS, and ENDCASE, and conditions are used to indicate the various alternatives. The general form is:
CASE expression OFindicating the value of "expression", but they can be English statements or some other notation that specifies the condition under which the given sequence is to be performed. A certain sequence may be associated with more than one condition.
condition 1 : sequence 1ENDCASEThe OTHERS clause with its default sequence is optional. Conditions are normally numbers or characters
condition 2 : sequence 2
...
condition n : sequence n
OTHERS:
default sequence
Example
CASE Title OF Mr : Print "Mister" Mrs : Print "Missus" Miss : Print "Miss" Ms : Print "Mizz" Dr : Print "Doctor" ENDCASE
Example
CASE grade OF A : points = 4 B : points = 3 C : points = 2 D : points = 1 F : points = 0 ENDCASE
REPEAT-UNTIL
This loop is similar to the WHILE loop except that the test is performed at the bottom of the loop instead of at the top. Two keywords, REPEAT and UNTIL are used. The general form is:
REPEATThe "sequence" in this type of loop is always performed at least once, because the test is peformed after the sequence is executed. At the conclusion of each iteration, the condition is evaluated, and the loop repeats if the condition is false. The loop terminates when the condition becomes true.
sequenceUNTIL condition
FOR
This loop is a specialized construct for iterating a specific number of times, often called a "counting" loop. Two keywords, FOR and ENDFOR are used. The general form is:
FOR iteration boundsIn cases where the loop constraints can be obviously inferred it is best to describe the loop using problem domain vocabulary.
sequenceENDFOR
Example
FOR each month of the year (good)
FOR month = 1 to 12 (ok)FOR each employee in the list (good)
FOR empno = 1 to listsize (ok)
NESTED CONSTRUCTS
The constructs can be embedded within each other, and this is made clear by use of indenting. Nested constructs should be clearly indented from their surrounding constructs.
Example
SET total to zeroIn the above example, the IF construct is nested within the REPEAT construct, and therefore is indented.
REPEAT
READ TemperatureUNTIL Temperature < zero
IF Temperature > Freezing THEN
INCREMENT total
END IF
Print total
INVOKING SUBPROCEDURES
Use the CALL keyword. For example:
CALL AvgAge with StudentAges
CALL Swap with CurrentItem and TargetItem
CALL Account.debit with CheckAmount
CALL getBalance RETURNING aBalance
CALL SquareRoot with orbitHeight RETURNING nominalOrbit
EXCEPTION HANDLING
BEGIN
statements
EXCEPTION
WHEN exception type
statements to handle exception
WHEN another exception type
statements to handle exception
END
Sample Pseudocode
FOR X = 1 to 10
FOR Y = 1 to 10
IF gameBoard[X][Y] = 0
Do nothing
ELSE
CALL theCall(X, Y) (recursive method)
increment counter
END IF
END FOR
END FOR
"Better"
Set moveCount to 1FOR each row on the board
FOR each column on the board
IF gameBoard position (row, column) is occupied THEN
CALL findAdjacentTiles with row, column
INCREMENT moveCount
END IF
END FOR
END FOR
(Note: the logic is restructured to omit the "do nothing" clause)
"Not So Good"
FOR all the number at the back of the array
SET Temp equal the addition of each number
IF > 9 THEN
get the remainder of the number divided by 10 to that index
and carry the "1"
Decrement one
Do it again for numbers before the decimal
SET Temp equal the addition of each number
IF > 9 THEN
get the remainder of the number divided by 10 to that index
and carry the "1"
Decrement one
Do it again for numbers before the decimal
"Good Enough (not perfect)"
SET Carry to 0
FOR each DigitPosition in Number from least significant to most significant
FOR each DigitPosition in Number from least significant to most significant
COMPUTE Total as sum of FirstNum[DigitPosition] and SecondNum[DigitPosition] and Carry
IF Total > 10 THEN
SET Carry to 1
SUBTRACT 10 from Total
ELSE
SET Carry to 0
END IF
SET Carry to 1
SUBTRACT 10 from Total
ELSE
SET Carry to 0
END IF
STORE Total in Result[DigitPosition]
END LOOP
IF Carry = 1 THEN
RAISE Overflow exception
END IF
RAISE Overflow exception
END IF
"Pretty Good" This example shows how pseudocode is written as comments in the source file. Note that the double slashes are indented.
public boolean moveRobot (Robot aRobot)
{
//IF robot has no obstacle in front THEN
// Call Move robot
// Add the move command to the command history
// RETURN true
//ELSE
// RETURN false without moving the robot
//END IF
}
{
//IF robot has no obstacle in front THEN
// Call Move robot
// Add the move command to the command history
// RETURN true
//ELSE
// RETURN false without moving the robot
//END IF
}
Example Java Implementation
- source code statements are interleaved with pseudocode.
- comments that correspond exactly to source code are removed during coding.
public boolean moveRobot (Robot aRobot)
{
//IF robot has no obstacle in front THEN
if (aRobot.isFrontClear())
{
// Call Move robot
aRobot.move();
// Add the move command to the command history
cmdHistory.add(RobotAction.MOVE);
return true;
}
else // don't move the robot
{
return false;
}//END IF
}
{
//IF robot has no obstacle in front THEN
if (aRobot.isFrontClear())
{
// Call Move robot
aRobot.move();
// Add the move command to the command history
cmdHistory.add(RobotAction.MOVE);
return true;
}
else // don't move the robot
{
return false;
}//END IF
}
Document History
| Date | Author | Change |
| 12/2/03 | JD | Added Exception Handling and more examples |
| 2/21/03 | JD | Added "problem domain vocabulary" paragraph. Modified FOR loop explanation. |
Loop: if we want to print all result then insert o/p box in loop…
if aggregate want to print then put o/p box out of the loop…
Pseudo code:
- "//" is used to represent the Comment.
- "begin ...end" use to start and end the Pseudo code.
- "accept" use to accept Input.
- "display" print Output.
- "if…. else" use to make decision.
- "repeat… un-till"
Pseudo code coding: Example
begin
numeric ' n num1, n num2, n sum'. (Variable)
Display 'enter first number'
Accept 'n num1'
Display 'second number'
Accept 'n num2'
n sum=n num1+n num2
Display' the sum is '+n sum..(+ concatenate operrator)
End
Q.1: Write Pseudo code that accept temperature in Celsius. Convert it into Fahrenheit and then displays the result ?
c/5=(f-32)/9
begin
numeric ntemp,nres
display 'enter temp in celsius'
accept 'ntemp'
nres=(9/5*ntemp)+32
display 'the temp in Fahrenheit is'+nres'.
end
Pseudo code: Product of two numbers…...
begin
numeric 'nnum1,nnum2,nproduct'(variable)
display 'enter first number'
accept 'nnum1'
display 'enter second number'
accept 'nnum2'
nproduct= nnum1*nnum2
display 'the product ' *nproduct'
end
Begin
Character cname
Display'enter name'
Accept cname
Display'Hello+cname'
end
Which on is largest?
begin
nummeric nnum1,nnum2,nnum3,nnum4,nnum5,ntemp
display 'enter five number'
accept nnum1,nnum2,nnum3,nnum4,nnum5
If nnum1>nnum2
begin
ntemp=nnum1
end
begin
ntemp=nnum2
end
if nnum3>ntemp
begin
ntemp=nnum3
end
else
begin
if ntemp<nnum4
begin
ntemp= nnum4
end
end
if nnum5>ntemp
begin
nnum5=ntemp
end
display'the largest number'+ntemp
end
Write a pseudocode to find out the percentage of a student in five subject and give him grade according to the following norms…
If %>= 90 Grade A
>= 75 B
>= 60 C
=< 60 D
Begin
Numeric nnum1, nnum2, nnum3, nnum4,nnum5,nsum,npercentage,ntotal
Character, cname
Display'name of the student'
Accept'cname'
Display'enter number of five subject'
Accept 'nnum1,nnum2,nnum3,nnum4,nnum5.'
nsum=nnum1+nnum2+nnum3+nnum4+nnum5
npercentage=(nsum/ntotal)*100
IfNpercentage >=90
begin
Display cGarde_A
end
Else
begin
If Npercentage>= 75
end
Begin
Display cgrade_B
End
Else
begin
ifNpercentage>= 60
end
Begin
Display cgrade_c
end
Else
Begin
Npercentage=<60
Begin
Display cgrade_d
End
End
Begin
Numeric nmarks,ntotal,navg,nctr
Nmarks=0
Ntotal=0
Navg=0
Nctr=0
Repeat
Begin
Enter'display the number of a student'
Accept nmarks
Ntotal=ntotal+nmarks
Nctr=nctr+1
End
Untill(nctr==30)
Navg=ntotal/30
Display the the avg marks of student'+navg'
end
