COP 2121 Program Development Process

Program Development Process

Program Specifications

• System analysts, users, and programmers develop specifications
• Specifications include:
  • Description of input and output data
  • Step-by-step processing required to convert input to output

Record layout forms describe format of input and output data

• Data names of each data item in record
• Location of each data item in record
• Size of each data item
• Number of decimal positions (for numerica data items)

Design the program

Program planning tools used to map out structure and logic of program

• Flowcharts use block diagrams to represent logic
• Pseudocode uses English-like statements
• Hierarchy charts show relationships among sections of program

Improving Program Design

Two techniques used to develop programs that are easier to understand, test, debug, and modify

• Structured Programming
• Top-Down programming

Structured Programming

Program divided into paragraphs

• Main paragraph or module control logic flow using PERFORM statements
• Main module "performs" other modules when instructions in that module are required
• Each module can be written and tested independently of others

Top-Down Programming

For COBOL program

• Code main modules or routines first
• Code intermediate modules next
• Details deferred to minor modules and coded last

Code and Enter Program

• Programmer writes and enters program into computer
• Program written in symbolic language (like COBOL)
• Called source program

Compile Source Program

Compiler is program that

• Checks source program for rule violations
• Translates source program into object program

Test Program

• Test or debug program to ensure it contains no errors
• Check for two types of errors
  • Compile-time errors
  • Execution errors

Compile-Time Errors

• Errors detected by compiler during translation from COBOL to machine language
• Detects violations of programming rules
  • Misspelled reserved words
  • Missing punctuation
• Also called syntax errors

Execution Errors

• Detected when program is run
• Logic error causes incorrect output
  • Sequence of instructions incorrect
  • Wrong instruction coded
• Run-time error if computer cannot execute instruction
  • Attempt to divide by zero
  • Attempt to read a file that cannot be found

Debugging Techniques

• Desk checking
• Correcting syntax errors
• Program walkthroughs
• Executing the program

Document the Program

• Documentation - formal set of procedures and instructions to specify how to use program
• Written for:
  • Those working with output
  • Computer operators who run program
  • Maintenance programmers who make modifications to program

Sample COBOL Program

IDENTIFICATION DIVISION.
PROGRAM-ID. WAGESBATCH.
ENVIRONMENT DIVISION.
INPUT-OUTPUT SECTION.
FILE-CONTROL. 	
		SELECT EMPLOYEE-DATA ASSIGN TO “/home/seemab/EMP-DAT.in".
		SELECT PAYROLL-LISTING ASSIGN TO “/home/seemab/EMP-OUT-DAT.out".

DATA DIVISION.
FILE SECTION.
FD	EMPLOYEE-DATA.
01	EMPLOYEE-RECORD.
	05	EMPLOYEE-NAME-IN		PIC X(20).
	05	HOURS-WORKED-IN		PIC 9(2).
	05	HOURLY-RATE-IN		PIC 9V99.

FD	PAYROLL-LISTING.
01	PRINT-REC.
	05				PIC X(20).
	05	NAME-OUT		PIC X(20).
	05				PIC X(10).
	05	HOURS-OUT		PIC 9(2).
	05				PIC X(8).
	05	RATE-OUT		PIC 9.99.
	05				PIC X(10).
	05	WEEKLY-WAGES-OUT	PIC 999.99.

WORKING-STORAGE SECTION.
01	ARE-THERE-MORE-RECORDS	PIC XXX VALUE "YES".
PROCEDURE DIVISION.
100-MAIN.
	OPEN 	 INPUT 	EMPLOYEE-DATA
		OUTPUT	PAYROLL-LISTING

	PERFORM UNTIL ARE-THERE-MORE-RECORDS = "NO"
		READ EMPLOYEE-DATA
			AT END
				MOVE 'NO ' TO ARE-THERE-MORE-RECORDS
			NOT AT END
				PERFORM 200-WAGE-ROUTINE
		END-READ
	END-PERFORM
	CLOSE  EMPLOYEE-DATA
		   PAYROLL-LISTING
	STOP RUN.

200-COMPUTE-WAGE-ROUTINE.
	MOVE SPACES TO PRINT_REC
	MOVE EMPLOYEE-NAME-IN TO NAME-OUT
	MOVE HOURS-WORKED-IN TO HOURS-OUT
	MOVE HOURLY-RATE-IN TO RATE-OUT
	MULTIPLY HOURLY-RATE-IN BY HOURS-WORKED-IN GIVING WEEKLY-WAGES-OUT
	WRITE PRINT-REC.