CMP 131 Introduction to Computer Programming

1. CMP 131Introduction to Computer Programming Violetta Cavalli-Sforza Week 4, Lecture 2

2. Homework #2Due Monday March 26 a) Textbook pg. 36 (Exercises 1.4): Do exercises 2, 4, 6, 7. b) Textbook pg. 44 (Exercises 1.5): Exercises 8, 13, 16. c) Following the example of calculating the mean that we used in class during Week 3 of the course, develop the problem statement, analysis, and design for a program that calculates the maximum of a set of numbers. You don't know how many numbers you will be given. You can assume that all numbers will be greater than 0.

3. Last Time • Started looking at some of the details of the Pascal programming language • Syntax graphs for describing legal syntax of various types of constructs • constants & literals • variables • Different kinds of identifiers and conventions for writing them: • reserved identifiers • standard identifiers • user-defined identifiers

4. Today • Homework #2 assigned • More programming language details • Data types and expressions

5. Special Symbols • Punctuation and other symbol combinations • Usually consists of one or two characters • Examples: • One character special symbols • Punctuation: . , ; : • Arithmetic: + - * / • Comparison, constant assignment: = • Two character special symbols • Variable Assignment: := • Comparison: <> <= >=

6. Statements • Executable Statements • Statements that appear in the program body, following the reserved word begin. • Each executable statement is translated by the compiler into one or more machine language instruction • Non-Executable Statements: • Statements that are not translated into machine language instructions and don't appear in the object file (declarations, begin-end, comments)

7. General Form of Pascal Programs program progName ; {Program heading} {Declaration part} const {Constants} constant = value; ... constant = value; type type1 = definition; ... type2 = definition; var {Variables} variable list : type; ... variable list : type; begin {Program body} statement; ... statement end.

8. Program Structure • Program heading: • Begins with the reserved word program • Tells the compiler the name of the program . • Declaration part: • Gives names and types of identifiers • Informs the compiler to reserve memory cells to them. • Program body: • Executable statements enclosed in begin-end.

9. program begin ( Identifier end . Identifier Statement ) ; ; , Program Structure • Program heading program pname; or program pname (Input, Output); • Program body begin statement(s) end.

10. Self-Check • Which of the following are valid program headings? Which are invalid and why? Program program; INVALID using reserved ID program 2ndCourseInCS; INVALID starts with digit program PascalIsFun; program Rainy Day; INVALID – contains space

11. General Form of Pascal Programs • begin & end enclose the program body • Semicolons (‘;’) separate statements • ‘;’ isn’t needed after begin or before end

12. Separators vs. Terminators • Separator: something that separates other itemsBEGIN a ; b ; c ; d ; … ; z END • Terminator: something that terminates another itemBEGIN [a ;] [b ;] [c ;] [d ;] … [z;] END • In Pascal, the proper use of ‘ ; ‘ is as a separator, but the compiler accepts it as a terminator.

13. One Pascal statement can extend over more than one line • More than one statement can be written on one line • Writing one statement per line improves the readability & simplifies program maintenance • Blankspace is mostly cosmetic. Pascal uses reserved words, punctuation, declarations and known statement types to understand your program.

14. Use of Blank Spaces • One or more blanks are considered as one blank • Tab is also considered as a blank • Blanks may be added to improve appearance of a program • Use blank lines between sections of a program • A blank is required between words in a program line • Leave a blank after comma, before and after operators (*, -, :=, ...).

15. Comments • Syntax: { comment } {New Pascal versions} or (* comment *) {Older Pascal versions} • Part of program documentation • Listed in the program but ignored by the Pascal compiler • Each program should begin with a header section that consists of a series of comments specifying: • Programmer's name and/or identification • Date of the current version of the program • Brief description of program purpose, use of identifiers, assumptions, prerequisites, . . . etc.

16. Self-Check • Rewrite the following code so that it has no syntax errors and follows the writing conventions we adopted Program SMALL; VAR X, Y, Z : real; BEGIN Y := 15.0; Z := -Y + 3.5; X :=Y + z; writeln (x, Y, z); END.

17. Program SMALL; VAR X, Y, Z : real; BEGIN Y := 15.0; Z := -Y + 3.5; x := Y + z; writeln (x, Y, z); END.

18. Self-Check PROGRM 2time5 {input,output}; CONST two := 2; five := 5; VAR multip; dummy ; integer; BEGIN ; multip = two * five ; dummy := multip ; write (two) , write (five) END ;

19. PROGRM p2time5 (input,output); CONST two = 2; five = 5; VAR multip, dummy : integer; BEGIN multip := two * five ; dummy := multip ; write (two) , write (five) END .

20. Pascal Data Types & Expressions

21. Pascal’s Standard Data Types • Predefined data types • real • integer • char • boolean for standard Pascal • strings ( added to Turbo Pascal) • Data types enable the compiler to know, for each memory cell used in a program • how much memory should be reserved • which operations are valid • The use of compile-time type-checking also allows many errors to be caught at compile-time.

22. Real Data Types • Floating-point : • A number representation consisting of: • A mantissa, M • An exponent, E • An (assumed) radix (or "base") • Sign bit. • The number represented is M*R^E where R is the radix - usually ten but sometimes 2. • Many different representations are used for the mantissa and exponent themselves. The IEEE specify a standard representation which is used by many hardware floating-point systems. • Fixed-point: • The fixed point of a function, f is any value, x for which f x = x. A function may have any number of fixed points from none (e.g. f x = x+1) to infinitely many (e.g. f x = x). The fixed point combinator, written as either "fix" or "Y" will return the fixed point of a function

23. Real Data Types • Objects: • Variables • Constants • Literals (i.e. value appearing directly in the program) • Operations: • Arithmetic: + - * / • Assignment: := • Standard procedures: ReadLn, WriteLn, Read, Write • Examples: Fixed-point Scientific Floating-point 12.345 1.2345 x 10 1.2345E1 12345.6 1.23456 x 104 1.23456E4 0.00012 1.2 x 10-4 1.2E-4 120000.0 1.2 x 105 1.2E5 -123000.0 -1.23 x 10-5 1.23E5

24. Self-Check • Write the following numbers in normal decimal notation: 103E-4 1.2345E+6 123.45E+3 • Write the following numbers in Pascal scientific notation 1300 123.45 0.00426

25. Ordinal Data Types • An ordinal data type is a data type whose values can all be listed • The following are ordinal data types • integer • boolean • char • Real data type is not ordinal - There are infinitely many real numbers and between any two real numbers there are infinitely many other real numbers