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Pascal

Pascal. Jinbo Lin. Pascal. Structured and Strong type language program HelloWorld; 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.

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Pascal

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  1. Pascal Jinbo Lin

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

  3. 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.

  4. 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.

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

  6. 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, int64. • The most common way, integer, will be stored as either smallint or longint.

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

  8. 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

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

  10. Control Structure Cont. 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. • 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

  11. SubProgram • Procedure vs Function • header, local declaration, body • pass by reference vs. pass by value function name(argument(s): type1; argument(s): type2; ...): function_type; local declarations; begin ... < statements > ... name:= expression; end;

  12. Support of Object-Oriented Programming • Object Pascal • Object vs. Class • Stack vs. Heap type object-identifier = object private field1 : field-type; field2 : field-type; ... public procedure proc1; function f1(): function-type; end;

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

  14. Exception Handling • Try • Except • Finally

  15. 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.

  16. 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

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

  18. 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.

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