Files Input and Output

Program Payroll_Calculator; Uses Crt, Printer; Const A_Payrate = 100.0; B_Payrate = 50.0; Var SS_personnel : string[9]; First_Name, Last_Name : String[20]; Paygrade : String[1]; Data_Line : String; Gross_Pay, Net_Pay, Withholding_Amount, SS_WithHolding_Amount,Deductions : Real; Gross_Pay_Accumulator : real; Personnel : Text; Found : Boolean; Blank_Location,error : Integer;

Begin clrscr; Assign(Personnel, 'A:\Personel.txt'); Reset(Personnel);

Reset opens a file to Read Rewrite opens a file to Write Rewrite erases any previous contents

Close(Personnel); End. (previous code)

Reading Input from a File Readln(Personnel, Data_line); File Variable variable

Reading Input that is Integer and/or Real Space is a delimitor Readln(Personnel, hours1, hours2, hours3)

String Input Size can be a delimitor Use String Functions to Separate

Writing to a File Writeln(Personnel,SS,blank,First_Name); File Variable Variables }

Writeln(lst,SS,blank,First_Name); Sends output to printer Variables } Don’t forget to include the ‘Uses Printer’ statement

Branching

Option A Option B Option C Evaluation of a condition

Conditions Equality Grade = A Greater Than A > B Lesser Than B < C

Truth Boolean Operators AND OR XOR NOT

(Grade = ‘A’) and (Class = ‘COP1000’) True

(Grade = ‘A’) or (Class = ‘COP1000’) With ‘or’ at least one must be true Expression or Condition

(Grade = ‘A’) XOR (Class = ‘COP1000’) With ‘XOR’ only one can be true -- not both Expression or Condition

(Not Grade = ‘A’) and (Class = ‘COP1000’) Not evaluates the expression and then gives it the opposite value. Expression or Condition

The IF Statement

IF THEN ELSE

IF Score > 90 THEN Letter_Grade := ‘A’; If the student’s grade is 91 or better, then the variable Letter_Grade will have a value of ‘A’. If the score is less than 91 then no value will be assigned to Letter_Grade

IF Score > 90 THEN Letter_Grade := ‘A’ ELSE Letter_Grade := ‘B’; This code means everyone will get an A or a B

IF Score > 90 THEN Letter_Grade := ‘A’ ELSE IF Score > 80 THEN Letter_Grade := ‘B’ ELSE IF Score > 70 THEN Letter_Grade := ‘C’ ELSE Letter_Grade := ‘D’;

No Punctuation before the ‘ELSE’

If Paygrade = 'A' then Begin (* Paygrade=A *) Gross_Pay := Hours_Worked * A_Payrate; Withholding_amount := Gross_Pay * A_withholding_Rate; End (* Paygrade=A *) else Begin (* Paygrade=B *) Gross_Pay := Hours_Worked * B_Payrate; Withholding_Amount := Gross_Pay * B_Withholding_Rate; end; (*Paygrade=B*) SS_Withholding_Amount := Gross_Pay * SS_Withholding_Rate; Deductions := SS_withholding_Amount + withholding_Amount; Net_pay := Gross_Pay - Deductions; Gross_Pay_Accumulator := Gross_Pay_Accumulator + Gross_Pay; Net_Pay_Accumulator := Net_Pay_Accumulator + Net_Pay; WH_Accumulator := WH_Accumulator + Withholding_Amount; SS_Accumulator := SS_Accumulator + SS_Withholding_Amount;

Vocabulary Iteration Procedures Procedure Calls Encapsulation

What do procedures do? Organize code by tasks Allows reusable code Protects values

Where do they fit? Program name; CONST VAR Procedure name Begin ____ End; Begin (*Program Body *) ____ _____ End;

Begins with the word Procedure Give the pocedure a name Procedure Open_Files; Begin Assign(Income, Data_File); End;

Begin Open_Files; Initialize_Count; While Not EOF(Income) DO Begin If Sex = ‘F’ Then Add_Females Else Add_Males; End; Compute_Averages; Output_Results; Close_Files; End; ‘Calling’ the Procedure

Naming a Procedure Usually, procedures have a verb indicating purpose of procedure Example: Calculate_Scores

Local Variables vs Global Variables

Global Variables Declared at the beginning of the program All procedures, all code recognizes global variables

Local Variables Declared within the procedure Known only within the procedure Protects against unintended consequences

Procedure Compare_Values ( VAR Val1 : integer; VAR Val2 : Real) ; Var I : Integer; Begin For I := 1 to Val1 DO Val2 := val2 + val1 End;

Parameters values that are passed to functions, procedures or other subprograms

Passing Parameters

What’s the difference ??? Reference, Formal or VAR parameters pass the address of the variable to the procedure. Thus any changes the procedure makes to the variable is passed back to the calling program. Value parameters pass a copy of the variable. Any changes the procedure makes to the value of the variable is not retained in the calling program.

Begin ________; ________: Compare_Values (Value1, Value2); ________; End. Parameters

Procedure Compare_Values ( VAR Val1 : integer; VAR Val2 : Real) ; Var I : Integer; Begin For I := 1 to Val1 DO Val2 := val2 + val1 End; Order is important. The parameters in the code which calls the procedure must be in the same order as the procedure

Value1 Val1 Val2 Value2 Procedure Call Make sure your data types are consistent

Begin Open_files; Initialize_Accumulators(WH_Total, SS_Total, Gross_Total, Net_Total); While not eof(Payroll) Do Begin (* payroll outer loop *) Readln(Payroll, Payroll_SS, Hours_Worked); Initialize_Inner_Loop; While (not eof(personnel)) and not found do Begin Readln(Personnel, dataline); Personnel_SS := dataline; If personnel_ss = payroll_SS then Begin Parse_Dataline (personnel_SS, First_Name, last_name, paygrade); ________ Formal Parameter

Procedure Parse_Data(DATA : STRING; VAR VAR FNAME, LNAME : String); CONST BLANK = ‘ ‘; VAR Blank Location : Integer; BEGIN Blank_Location := POS(Data,Blank); FNAME := COPY(DATA,1,Blank_Location -1); Delete(Data, 1, Blank_Location); LNAME := DATA; END; Value Actual Local

Scope

Definition Scope concerns the visability of variables

Program Example; VAR X : Integer; Procedure A; VAR y : Integer; Procedure B Var z : Integer; Begin (*Procedure B *) ____ End; (*Procedure B *) Begin (* Procedure A *) End; (* Procedure A *) Begin (*Program Code *) X Y Z Scope of Each Variable

Functions

Differences Between Functions and Procedures Procedures capable of returning to the calling program more than one value. Functions return only one value.

Function Parse_Name(Data : String) : String Keyword Function Name Parameters Data type of value the function returns

Important! A function does not automatically assign a value to a variable. You must program it that way

FIRST_NAME := COPY(DATA, 1, POS(DATA,BLANK) -1) Blank_Location := POS(DATA,BLANK); FIRST_NAME := COPY(DATA,1,Blank_Location-1) note: the second method does not store the location of the blank in a variable. It can not be used later in the program.

Recursion A function which calls itself

That’s Enough

The End