Program Design Language (PDL)

Program Design Language (PDL)

Program Design Language (PDL), also known as pseudocode, is a structured, English-like language used to express the logic of a program or module before actual coding begins. It bridges the gap between design documents and implementation code.

PDL Constructs

Sequence:
    statement 1
    statement 2
    statement 3

IF-THEN-ELSE:
    IF condition THEN
        action
    ELSE IF condition THEN
        action
    ELSE
        action
    ENDIF

WHILE Loop:
    WHILE condition DO
        action
    ENDWHILE

FOR Loop:
    FOR index = start TO end DO
        action
    ENDFOR

REPEAT-UNTIL:
    REPEAT
        action
    UNTIL condition

CASE:
    CASE expression OF
        value1: action
        value2: action
        DEFAULT: action
    ENDCASE

PDL Example: Student Grade Calculator

MODULE CalculateGrade

    INPUT: studentMarks

    IF studentMarks >= 90 THEN
        grade = "A"
    ELSE IF studentMarks >= 80 THEN
        grade = "B"
    ELSE IF studentMarks >= 70 THEN
        grade = "C"
    ELSE IF studentMarks >= 60 THEN
        grade = "D"
    ELSE
        grade = "F"
    ENDIF

    IF grade == "F" THEN
        WRITE "Student must retake the course"
    ELSE
        WRITE "Congratulations! Grade:", grade
    ENDIF

END MODULE

PDL vs Pseudocode vs Programming Language

Benefits of Using PDL

• Forces designers to think through logic before coding
• Easy to read and understand by non-programmers
• Language-independent (not tied to any specific programming language)
• Facilitates early review and debugging of logic
• Serves as documentation for the implemented code

Summary

PDL is a powerful design tool that helps analysts and developers express program logic clearly and consistently. It improves code quality by encouraging thorough design before implementation.