Structured Programming Language ITSS 113 Lecture1 INTRODUCTION Learning

Structured Programming Language ITSS 113

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

Introduction to COBOL • COBOL – Common Business Oriented Language – 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 .

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 fileoriented, applications, and is not designed for writing systems programs. • Primary domain in business, finance, and administrative systems for companies and governments.

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

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

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.

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

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

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

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

Character Set There are 50 different characters in COBOL character set. 0 -9 A-Z – + * / = $ , ; . “ (10 numerals) (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)

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.

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

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.

COBOL WORDS (continued) Examples Valid Word Invalid Word Reason emp-sal NET-SAL N 100 -pay TOTAL MARK COMPUTE 23 (it starts with a hyphen) (blank space embedded) (Reserved word) (No letter)

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.

Literals (continued) There are 3 types of literals: a) 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.

Literals (continued) Figurative Constant Meaning ZEROS ZEROES value 0 SPACES One or more blanks HIGH-VALUES Highest value in the Collating sequence LOW-VALUES Lowest value in the Collating sequence QUOTES one or more of “ ALL literal one or more of the string characters comprising the literal

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