Pascal Jinbo Lin Pascal Structured and Strong type

Pascal Jinbo Lin

Pascal • Structured and Strong type language • program Hello. World; • uses crt; • var x: string='Hello, World!'; • begin • writeln(x); • readkey; • end.

History • Pascal is a programming language that grew out from ALGOL. • Published by Dr. Niklaus Wirth in 1971. • Designed as a teaching programming language. • Later, Dr. Ken Bowles in UCSD adapt the Pascal compiler to Apple II. • By early 1980's, U. S. Educational Testing Service decide to add a computer science AP Exam, Pascal was chosen. • In 1999, C++ replaced Pascal, and Java replaced C++ soon after that.

Names, Binding, and Scopes • Pascal is case insensitive. • letters, digits, and _ are only characters allowed to make identifiers. • Different types of compiler has its own rules on the length of identifier name. • Static Binding • All ALGOL based language are static scoping, which includes Pascal.

Data Types • Simple : – – – integer real character boolean user-defined type • Structured: – – array record file set • Pointer.

Data Types (Integer) • Pascal has many ways to define those data types, and each type may be vary on the range and the memory size. • Ten types of Integer: – – byte : 0 to 255, 1 byte smallint: -(2^15) to (2^15) -1, 2 bytes longint: -(2^31) to (2^31)-1 , 4 bytes ingeter, shortint, word, cardinal, qword, longword, int 64. • The most common way, integer, will be stored as either smallint or longint.

Data Types (String) • String: – character array: a sequence of zero or more characters enclosed by single quotes. (e. g. my. String: pack array [1. . 20] of char) – string: a sequence of characters with an optional size specification. (e. g. my. String: string) – short string: a string type that with the specification of length (e. g. my. String: string[20]) – null terminated string: use a null value at the end of actual string value to indicate the length (e. g. my. String: pchar)

Expressions and Assignment Statements • operator precedency rule is the same as other language • Strict type checking • Only two exception: – implicit data type conversion within same group – implicit data type conversion with int and real. • Pascal Support Operator Overloading

Control Structure • Selection – if then else – case • Iteration – for do – while do – repeat until • key word: break, continue.

Control Structure Cont. • Goto: statement that provides an unconditional jump from the goto to a labeled statement in the same function. • • value of i: 1 value of i: 2 value of i: 3 value of i: 4 value of i: 5 value of i: 6 value of i: 8 value of i: 9 program example; uses crt; label 1; var i : integer; begin i : = 1; 1: repeat if( i = 7) then begin i : = i + 1; goto 1; end; writeln('value of i: ', i); i: = i +1; until i = 10; readkey; end.

Sub. Program • Procedure vs Function • header, local declaration, body • pass by reference vs. pass by value function name(argument(s): type 1; argument(s): type 2; . . . ): function_type; local declarations; begin. . . < statements >. . . name: = expression; end;

Support of Object-Oriented Programming • Object Pascal • Object vs. Class • Stack vs. Heap type object-identifier = object private field 1 : field-type; field 2 : field-type; . . . public procedure proc 1; function f 1(): function-type; end;

Concurrency • Concurrent Pascal, or Pascal FC • Constructs that are removed: – records – goto statement and labels – procedures as parameter – packed arrays – pointer types – file types.

Exception Handling • Try • Except • Finally

Readability • Pros: – Code is structured – Simplicity: not flexible – More English words than symbols • Cons: – Too many ways to define a data type like string and integer. – use begin. . end instead of {. . } • Conclusion: high readability.

Writability • Pros: – Case Insensitive – Operator Overloading – Abstract data types • Cons: – More English words than symbols – Lack of flexibility – Relatively less API available • Conclusion: decent Writability

Reliability • Pros: – Strongly typed – Support for exception handling – Rich data types set • Cons: – Aliasing: pointer and pass by reference mode • Conclusion: super reliable

Cost • Software: two major IDE: Lazarus and Delphi, are free to download online. • Hardware: Lazarus is a cross-platform IDE that can run on Windows, Linux and Mac. • Overall: Pascal has high readability, decent writability, and it is super reliable. The price is, Pascal is not powerful.