--- language: Pascal filename: learnpascal.pas contributors: - ["Ganesha Danu", "http://github.com/blinfoldking"] - ["Keith Miyake", "https://github.com/kaymmm"] --- >Pascal is an imperative and procedural programming language, which Niklaus Wirth designed in 1968–69 and published in 1970, as a small, efficient language intended to encourage good programming practices using structured programming and data structuring. It is named in honor of the French mathematician, philosopher and physicist Blaise Pascal. source : [wikipedia](https://en.wikipedia.org/wiki/Pascal_(programming_language)) To compile and run a pascal program you could use a free pascal compiler. [Download Here](https://www.freepascal.org/) ```pascal //Anatomy of a Pascal Program //this is a comment { this is a multiline comment } //name of the program program learn_pascal; //<-- don't forget a semicolon const { this is where you should declare constant values } type { this is where you should declare custom data-types } var { this is where you should declare a variable } //main program area begin { area to declare your instruction } end. // End of a main program area should require a "." symbol ``` ```pascal //When declaring variables //you can do this var a:integer; var b:integer; //or this var a : integer; b : integer; //or this var a,b : integer; ``` ```pascal program Learn_More; //Let's learn about data types and their operations const PI = 3.141592654; GNU = 'GNU''s Not Unix'; // constants are conventionally named using CAPS // their values are fixed and cannot be changed during runtime // holds any standard data type (integer, real, boolean, char, string) type ch_array : array [0..255] of char; // arrays are new 'types' specifying the length and data type // this defines a new data type that contains 255 characters // (this is functionally equivalent to a string[256] variable) md_array : array of array of integer; // nested arrays are equivalent to multidimensional arrays // can define zero (0) length arrays that are dynamically sized // this is a 2-dimensional array of integers //Declaring variables var int, c, d : integer; // three variables that contain integer numbers // integers are 16-bits and limited to the range [-32,768..32,767] r : real; // a variable that contains a real number data types // reals can range between [3.4E-38..3.4E38] bool : boolean; // a variable that contains a Boolean(True/False) value ch : char; // a variable that contains a character value // char variables are stored as 8-bit data types so no UTF str : string; // a non-standard variable that contains a string value // strings are an extension included in most Pascal compilers // they are stored as an array of char with default length of 255. s : string[50]; // a string with maximum length of 50 chars. // you can specify the length of the string to minimize memory usage my_str: ch_array; // you can declare variables of custom types my_2d : md_array; // dynamically sized arrays need to be sized before they can be used. // additional integer data types b : byte; // range [0..255] shi : shortint; // range [-128..127] smi : smallint; // range [-32,768..32,767] (standard Integer) w : word; // range [0..65,535] li : longint; // range [-2,147,483,648..2,147,483,647] lw : longword; // range [0..4,294,967,295] c : cardinal; // longword i64 : int64; // range [-9223372036854775808..9223372036854775807] qw : qword; // range [0..18,446,744,073,709,551,615] // additional real types rr : real; // range depends on platform (i.e., 8-bit, 16-bit, etc.) rs : single; // range [1.5E-45..3.4E38] rd : double; // range [5.0E-324 .. 1.7E308] re : extended; // range [1.9E-4932..1.1E4932] rc : comp; // range [-2E64+1 .. 2E63-1] Begin int := 1;// how to assign a value to a variable r := 3.14; ch := 'a'; str := 'apple'; bool := true; //pascal is not a case-sensitive language //arithmetic operation int := 1 + 1; // int = 2 overwriting the previous assignment int := int + 1; // int = 2 + 1 = 3; int := 4 div 2; //int = 2 division operation where result will be floored int := 3 div 2; //int = 1 int := 1 div 2; //int = 0 bool := true or false; // bool = true bool := false and true; // bool = false bool := true xor true; // bool = false r := 3 / 2; // a division operator for real r := int; // can assign an integer to a real variable but not the reverse c := str[1]; // assign the first letter of str to c str := 'hello' + 'world'; //combining strings my_str[0] := 'a'; // array assignment needs an index setlength(my_2d,10,10); // initialize dynamically sized arrays: 10×10 array for c := 0 to 9 do // arrays begin at 0 and end at length-1 for d := 0 to 9 do // for loop counters need to be declared variables my_2d[c,d] := c * d; // address multidimensional arrays with a single set of brackets End. ``` ```pascal program Functional_Programming; Var i, dummy : integer; function factorial_recursion(const a: integer) : integer; { recursively calculates the factorial of integer parameter a } // Declare local variables within the function // e.g.: // Var // local_a : integer; Begin If a >= 1 Then // return values from functions by assigning a value to the function name factorial_recursion := a * factorial_recursion(a-1) Else factorial_recursion := 1; End; // terminate a function using a semicolon after the End statement. procedure get_integer(var i : integer; dummy : integer); { get user input and store it in the integer parameter i. parameters prefaced with 'var' are variable, meaning their value can change outside of the parameter. Value parameters (without 'var') like 'dummy' are static and changes made within the scope of the function/procedure do not affect the variable passed as a parameter } Begin write('Enter an integer: '); readln(i); dummy := 4; // dummy will not change value outside of the procedure End; Begin // main program block dummy := 3; get_integer(i, dummy); writeln(i, '! = ', factorial_recursion(i)); // outputs i! writeln('dummy = ', dummy); // always outputs '3' since dummy is unchanged. End. ```