#3 Pseudocode || Programming basics

 PseudoCode

PseudoCode

• Pseudo code is a kind of structured English for representing algorithms.
• Pseudo code is a text based detailed design tool for human understanding.

Basic Guidelines

• Statements should be written in simple English.
• Steps must be understandable and when the steps are followed they should produce the solution.
• Pseudo code should be concise.
• Capitalize keywords like READ, PRINT, and so on.

Keywords Used

• Input : READ, INPUT, OBTAIN, GET
• Output : PRINT, OUTPUT, DISPLAY
• Compute : COMPUTE, CALCULATE
• Initialize : SET, INIT
• Add one : INCREMENT

Basic constructs of Pseudocode

• Sequence
• Selection
• Repetition

Sequence

            Each statement in the program is executed one after another in the given order. The statements are executed sequentially from top to bottom

Pseudocode to add two numbers

READ a,b

CALCULATE sum=a+b

PRINT sum

Selection

            It is a decision in which a choice is made between two alternative choices of actions. It consists of 2 types.

• IF…THEN…ELSE
• CASE…ENDCASE

(1)IF…THEN…ELSE

             Binary choice on a given Boolean condition is indicated by the use of four keywords:

IF, THEN, ELSE and ENDIF

Syntax:

IF condition THEN

          sequence1

ELSE

          sequence2

ENDIF

Pseudocode to check whether the number is odd or even

READ n

IF n MOD 2 = 0 THEN

PRINT “The number is even”

ELSE

PRINT “The number is odd”

ENDIF

(2)CASE…ENDCASE

             CASE is a multiway branch based on the value of an expression. Four keywords are used:

CASE, OF, OTHERS and ENDCASE.

Syntax:

CASE expression OF

condition1:sequence 1

condition2:sequence 2

…………………………

condition n:sequence n

OTHERS:

default:sequence

ENDCASE

Pseudocode for simple calculator

READ num1, num2, choice

CASE choice OF

+ : PRINT num1 + num2

- : PRINT num1 – num2

* : PRINT num1 * num2

/ : PRINT num1 / num2

ENDCASE

Repetition

It is a loop based on the satisfaction of some conditions. It consists of 3 constructs.

• WHILE…ENDWHILE
• REPEAT…UNTIL
• FOR…ENDFOR

(1)WHILE…ENDWHILE

             It is a loop based on a simple condition at the beginning. The beginning and ending of the loop is indicated by the keywords WHILE and ENDWHILE.

The loop is entered only if the condition is true. The sequence is performed for each iteration. At the end of each iteration, the condition is executed and the loop continues as long as the condition is true.

Syntax:

WHILE condition

sequence

ENDWHILE

Pseudocode to print number from 1 to 100

SET n=1

WHILE n is less than or equal to 100

DISPLAY n

INCREMENT n by 1

ENDWHILE

(2) REPEAT…UNTIL

It is loop with a simple condition at the bottom. It is similar to WHILE loop except that the test is performed at the bottom of the loop.

The sequence is performed at least once because the condition is evaluated after the sequence is performed. At the end of each iteration, the condition is evaluated and the loop repeats if the condition is false. The loop ends when the condition become true.

Syntax:

REPEAT

sequence

UNTIL condition

Pseudocode to print number from 1 to 100

SET n=1

REPEAT

DISPLAY n

INCREAMENT n by 1

UNTIL n is greater than 100

(3) FOR…ENDFOR

For is counting loop. The loop is used for interating a specific number of times. The keywords used are FOR and ENDFOR.

Syntax:

FOR iteration bounds

sequence

ENDFOR

Pseudocode to print number from 1 to 100

FOR n=1 to 100

DISPLAY n

ENDFOR

ADVANTAGES

• Can be read and understood easily.
• Can be modified easily.

DISADVANTAGES

• Creates an additional level of documentation to maintain
• Introduces error possibilities.