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---
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
//Anathomy of a Pascal Program
//this is a comment
{
this is a
multiline comment
}
//name of the program
program learn_pascal; //<-- dont forget a semicolon
const
{
this is where you should declare constant values
}
type
{
this is where you should delcare a 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 required a "." symbol
```
```pascal
//declaring variable
//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;
//Lets 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
//arithmethic 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.
```
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