So now we’re programming

What do programs do? Manipulate (process) data Math Read files Write to files Create files

Good programmers Always Always start with pseudocode See page100

Programs must be named You choose the name It must be one word follow with a semi-colon Example: Program First_Program ;

Next, type program comments Program First_Program; (***********************************) (* Program: First.pas *) (* Programmer: Sue Halfhill *) (* Date: September, 1999 *) (* Description: Program is a point of sale *) (* system *) (***********************************)

Next, declare any constants Constants do not change value Program First_Program; (***********************************) (* Program: First.pas *) (* Programmer: Sue Halfhill *) (* Date: September, 1999 *) (* Description: Program is a point of sale *) (* system *) (***********************************) CONST Multiplier = 5;

Next, declare any variables Program First_Program; (***********************************) (* Program: First.pas *) (* Programmer: Sue Halfhill *) (* Date: September, 1999 *) (* Description: Program is a point of sale *) (* system *) (***********************************) VAR Fname : String[15]; Lname : String[25]; Sum, X, Y : Integer;

String Variables Contain alpha-numeric data Are 256 bytes in size unless declared –Use [ ] to declare smaller size

Char One byte only in size Byte Either True or False

Integers vs Real Whole numbers Legal values of - 32,768 to 32,767 Use LongInt for larger numbers +, -, *, div, MOD Must have decimals Can be used for exponents Maximum value determined by computer memory +, -, *, /

Integer vs Real Real Integer

Implications Integers variables can be assigned to Real Variables Real variables can not be assigned to Integer variables

Next Code must start with Begin and finish with End. Program First_Program; (***********************************) (* Program: First.pas *) (* Programmer: Sue Halfhill *) (* Date: September, 1999 *) (* Description: Program is a point of sale *) (* system *) (***********************************) VAR Fname : String[15]; Lname : String[25]; Sum, X, Y : Integer; Begin ====== End.

Putting values into variables Sum := 2 + 4; FName := ‘John’; Variable Name Assignment Operator Literal or Value being stored

Assigning Values Program First_Time; CONST Multiplier = 5; VAR Fname : String[15]; Lname : String[25]; Sum, Sum, X, Y : Integer; Begin X := 2; Y := 6; Sum := Multiplier(X + Y); Writeln(Sum); End;

How ‘Hard Code’ User Input Read from a file OH- OH

Read Procedure Read(parameter,parameter) Readln(parameter,pararmeter) Reading numeric data vs string data

Read(parameter,parameter) 7 5 Read(A,B) Space is a delimiter (separator) for integer or real data 7 5 With the read procedure the marker does not go to the next line

Readln(parameter,parameter) 7 5 Readln(A, B) With the readln procedure the marker goes to the next line

String Variables vs Read/Readln The size of A and B determine how much is read Dataline : string[9] reads up to 9 characters (letters, spaces, numbers, etc)

Write/Writeln Cursor similar to Read/Readln; Directs data to –screen Writeln(‘What is your name’); –to file Writeln(filename, Sum); –to printer Writeln(lst, ‘What is your name?’);

What’s A Function Black Box Command Result X := Length(Data_line) ;

String Functions

Begin Writeln(‘Please enter your social security number.’) Read(SSNumber); Writeln(‘Please enter your first name and last name.’) Readln(Data_line); X := Length(Data_line); Y := POS(Blank,Data_line); First_Name := COPY(Data_Line,1,y-1); Delete(Data_Line,1,y); X := Length(Data_Line); Last_Name := Data_line; End.

X := Length(Data_line) ; Y := POS(Blank, Data_line) ; First_Name := COPY(Data_line, 1, 5) ; Delete(Data_line, 1, y) ;

X := Length(Data_line); Anatomy of a Function Function Name Parameters Variable which holds value

X := Length(Data_line) ; Sue Halfhill Data_Line X = 12

Y := POS(Blank, Data_line) ; Sue Halfhill Blank Y = 4 2 parameters !!!!

First_Name := COPY(Data_line, 1, 3) ; First_Name Sue Halfhill Data_line } 3 1 Sue 3 parameters !!!!

Delete Delete(Data_line,1,y)

Math Functions Round Trunc Sqr Sqrt Str

STR(X,S) X is an integer or real value X must be formatted. X:4:2 S is a string variable.