Chapter 1.  Pascal Preliminaries

A Brief Review of Pascal

Form of a Pascal Program

  program<program-name> (INPUT,OUTPUT);
    {<declaration section>}
    procedure A;
    procedure B;
    begin
      {<executable-statements>}
      A;
      {<executable-statements>}
      B;
      {<executable-statements>}
    end.

Form of a Pascal Procedure or Subroutine

  procedure <procedure-name> [(<formal-parameter-list>)]
    {<local declaration section>}
    begin
      {<executable-statements>} i.e. procedure body
    end;

Form of a Call to a Procedure.

  <procedure-name>[<actual-parameter-list>]

Form of a Pascal function

  function <function-name> [(<formal-parameter-list>)]: result-type;
    {<local declaration section>}
    begin
    {<executable-statements>} i.e. function body
    end;

Specification Statements (Declaration Part)

  label
    999;

  const
    Max = 10;
    Pi = 3.1415926535;
    Small = 1e-20;

  type
    Subs = 1..Max;
    VECTOR = array[1..5] of real;
    MATRIX = array[1..5,1..5] of real;
    POINTER = array[Subs] of integer;
    STATUS = (Done,Iterating,Working);
    WORDS = string[80];


  var
    Column,I,J: integer;
    A0,B0,Max,X,Y: real;
    Flag: boolean;
    V,R: VECTOR;
    A,D: MATRIX;
    Row: POINTER;
    Name: string[80];
    Lines: WORDS;
    State: STATUS;

Assignment Statements

  X := A[1] + 3;
  Y := A*X*X + B*X + C;
  Flag := true;
  Name := 'Fran';

Arithmetic Operations

  +  Addition
  -  Subtraction
  *  Multiplication
  /  Division
  div  Integer Division
  mod  Remainder (Integer)

Relational Operators

  =  Equal to
  <>  Not equal to
  <  Less than
  >  Greater than
  <=  Less than or equal to
  >=  Greater than or equal to

Logical Operators

  not  Complement
  and  True if both operands are true
  or  True if either (or both) operands are true

Logical Constants

  true
  false

Remark Statement

  {This is a comment.}

Place-holder Statement (or label)

  100:


Unconditional Transfer

  goto 100;

  Warning. A GOTO statement must not leave the current block.

IF (Block) Control Statement

Performs the series of {<executable-statement>} following it or transfers control to an else, or end statement, depending on the value of the (<logical-expression>).

  if (<logical-expression>) then
    {<one executable-statements>};

  if (<logical-expression>) then
    begin
      {<one executable-statement>}
    end;

  if (<logical-expression>) then
    {<one executable-statement>}
  else
    {<one executable-statement>};


  if (<logical-expression>) then
    begin
      {<executable-statements>}
    end
  else
    begin
      {<executable-statements>}
    end;

  if (<logical-expression-#1>) then
    begin
      {<executable-statements>}
    end
  else 
    begin
      if (<logical-expression-#2>) then
        begin
          {<executable-statements>}
        end
      else
        begin
          {<executable-statements>}
        end;
    end;

Indexed Loop Control Statement

  Sum := 0;
  for  k := 0  to  100  do
    Sum := Sum + k;

  Sum := 0;
  for  k := 1000  downto  1  do
    Sum := Sum + 1.0/k;

  for  j := 1  to  5  do
    for  k := 1  to  5  do
      A[j,k] := 1.0/(j+k-1);

While Loop Structure
  The <logical-expression> is evaluated first.  If the logical expression is true, then the loop body will be executed.  The sequence is repeated as long as the expression remains true.  If the expression is false, then the loop body will be skipped, and execution will continue with the statement following  end;.

  while (<logical-expression>) do
    begin
      {<executable-statements>}
    end

Case Statement

  Case  FunType
    1: F := x;
    2: F := x*x;
  else
    F := x*x*x;
  end;

Input and Output

  readln(x,y);
  readln(A[i,j]);

  writeln;
  writeln('x = ',x,'     y = ',y);
  write  ('A(i,j) = ',A[i,j]:15:5);

Mathematical Functions

  cos(x)  cosine (radians)
  sin(x)  sine (radians)
  exp(x)  exponential  exp(x)
  arctan(x)  inverse tangent (radians)
  ln(x)  natural logarithm base  e
  sqrt(x)  square root
  sqr(x)  the square of a number
  abs(x)  absolute value
  int(x)  real valued greatest integer function
  trunc(x)  integer valued greatest integer function
  round(x)  the closest integer value