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Structured Programming Language COBOL

Structured Programming Language COBOL. Lecture-1 : INTRODUCTION. Learning Objectives:. To provide brief history of COBOL To learn the capabilities and limitations of COBOL To present the program layout of COBOL To discuss the structure of a COBOL program

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Structured Programming Language COBOL

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  1. Structured Programming Language COBOL

  2. Lecture-1 : INTRODUCTION Learning Objectives: • To provide brief history of COBOL • To learn the capabilities and limitations of COBOL • To present the program layout of COBOL • To discuss the structure of a COBOL program • To determine the difference between COBOL Literal Set, COBOL Words, COBOL Literals

  3. Introduction to COBOL • COBOL • CommonBusinessOrientedLanguage • A third-generation programming language, • Was one of the earliest high-level programming languages; still widely used today. • First proposed in 1959 by the Conference on Data Systems Languages (CODASYL). • Three ANSI standards for COBOL have been produced in 1968, 1974 and 1985. • Object-oriented COBOL is the fourth edition in the continuing evolution of ANSI/ISO standard COBOL.

  4. Underlining Philosophy • Like the name suggests, COBOL was meant to be ‘common’ or compatible among a significant group of manufacturers • COBOL is designed for developing business, typically file-oriented, applications, and is not designed for writing systems programs. • Primary domain in business, finance, and administrative systems for companies and governments.

  5. Pro’s and Con’s • Advantages • Simple • Portable • Maintainable • Disadvantages • very wordy • has a very rigid format • not designed to handle scientific applications

  6. Distinct features • The language is simple • No pointers • No user defined types • No user defined functions • ‘Structure like’ data types • File records are also described with great detail, as are lines to be output to a printer • COBOL is self documenting

  7. COBOL program layout The layout, or format, or a COBOL program follows certain simple rules, which originated long ago when programs were punched onto 80-column punch cards. COBOL programs are written in coding sheets. There are 80 columns in a line of the coding sheet.

  8. COBOL program layout (continued) Column Field 1-3 Page Number 4-6 Line Number (1-6 Sequence Number) 7 Continuation / Comment 8-11 A – Margin / Area A 12-72 B- Margin /Area B 73-80 Identification

  9. Structure of COBOL Program • COBOL programs are hierarchical in structure. • Each element of the hierarchy consists of one or more subordinate elements. • The levels of hierarchy are Divisions, Sections, Paragraphs, Sentences and Statements • There are 4 main divisions and each division provides an essential part of the information required by the complier

  10. Structure of COBOL Program (continued) • At the top of the COBOL hierarchy are the four divisions. • The sequence in which they are specified is fixed, and must follow the order: • IDENTIFICATION DIVISION.This division’s primary purpose is to name the program • ENVIRONMENT DIVISION. This division is primarily used to tell the computer about the input and output devices such files or printers. • DATA DIVISION provides descriptions of the data-items/fields processed by the program. • PROCEDURE DIVISION contains the code used to manipulate the data described in the DATA DIVISION. It is here that the programmer describes his algorithm. • Note: • Some COBOL compilers require that all the divisions be present in a program while others only require the IDENTIFICATION DIVISION and the PROCEDURE DIVISION

  11. Hello World Example 000100 IDENTIFICATION DIVISION. 000200 PROGRAM-ID. HELLOWORLD. 000300 000400 ENVIRONMENT DIVISION. 000500 CONFIGURATION SECTION. 000600 SOURCE-COMPUTER. RM-COBOL. 000700 OBJECT-COMPUTER. RM-COBOL. 000800 000900 DATA DIVISION. 001000 FILE SECTION. 001100 101200 PROCEDURE DIVISION. 101300 101400 MAIN-LOGIC SECTION. 101500 DISPLAY "Hello world!" 101600 STOP RUN.

  12. Character Set There are 50 different characters in COBOL character set. 0-9 (10 numerals) A-Z (26 English alphabets-only capital letters) – (minus sign or hyphen) + (Plus sign) * (Asterisk) / (Slash) = (Equal sign) $ (Currency sign) , (Comma) ; (Semi colon) . (Period or decimal point) “ (Quotation mark) ( (Left Parenthesis ) ) (Right Parenthesis) > (Greater than symbol) < (Less than symbol)

  13. Character Set (continued) The characters 0-9 are called numeric characters or digits. The characters A-Z are called letters The remaining characters are called special characters. The space or blank character in certain cases is treated as a letter.

  14. COBOL WORDS A COBOL word can be formed using the following characters: 0-9 A-Z (a-z) - (hyphen) There are 2 types of words in COBOL: 1.) Reserved word 2.) User-defined word

  15. COBOL WORDS (continued) • Paragraph names, Identifiers, File names can be defined by users. The following rules must be adhered in forming COBOL user-defined words: 1.) A word cannot begin or end with a hyphen. 2.) A word can have at the maximum 30 characters. 3.) One of the characters must be a letter. (Some compilers put the additional restrictions that the first character must be a letter.) 4.) Except hyphen (-) no special character allowed. 5.) Cannot be a COBOL reserved word.

  16. COBOL WORDS (continued) Examples Valid Word Invalid WordReason emp-sal -pay (it starts with a hyphen) NET-SAL TOTAL MARK (blank space embedded) N100 COMPUTE (Reserved word) 23 (No letter)

  17. Literals The actual values can also appear in a program. Such values are known as literals. A data name may have different values at different points of time whereas a literal means the specific value which remains unchanged throughout the execution of the program. For this reason a literal is often called a constant. Moreover the literal is not given a name; it represents itself and does not require to be defined in the DATA DIVISION.

  18. Literals (continued) • There are 3 types of literals: • Numeric. Formed by digits only. It can have a sign (+ or -) and can have a decimal point also. • b) Nonnumeric. Use in general to output messages or • headings. Characters that are enclosed between “ “ • constitute nonnumeric literal. • c) Figurative Constants. Have some fixed names and • the compiler recognizes these names and it sets up • corresponding values in the object program.

  19. Literals (continued)

  20. Summary • Brief history or COBOL • Underlining Philosophy of COBOL • Distinct Features of COBOL • COBOL Program Layout • Structure of COBOL program • Character Set • COBOL Words • Literals Summary of the chapter or topic

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