| .Selected Input/Output Example Programs. |
|
 Selected Programs I/O Programs Contents Index |
| ÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄ |
| File and Device I/O |
| |
| The following programming examples illustrate how to code file I/O and |
| device I/O statements. |
| |
| Example 1 - Sequential File I/O |
| |
| The following short program creates a sequential file named "Price.Dat," |
| then adds data entered at the keyboard to the file. The OPEN statement |
| in this program both creates the file and readies the file to receive |
| records. The WRITE # then writes each record to the file. Note that the |
| number used in the WRITE # statement is the same number given to the |
| file name Price.Dat in the OPEN statement. |
| |
| ' Create a file named Price.Dat |
| ' and open it to receive new data: |
| |
| OPEN "Price.Dat" FOR OUTPUT AS #1 |
| |
| DO |
| ' Continue putting new records in Price.Dat until the |
| ' user presses ENTER without entering a company name: |
| ' |
| INPUT "Company (press <> to quit): ", Company$ |
| |
| IF Company$ <> "" THEN |
| ' Enter the other fields of the record: |
| INPUT "Style: ", Style$ |
| INPUT "Size: ", Size$ |
| INPUT "Color: ", Clr$ |
| INPUT "Quantity: ", Qty |
| ' Put the new record in the file |
| ' with the WRITE # statement: |
| WRITE #1, Company$, Style$, Size$, Clr$, Qty |
| END IF |
| LOOP UNTIL Company$ = "" |
| ' Close Price.Dat (this ends output to the file): |
| CLOSE #1 |
| END |
| |
| Example 2 - Sequential File I/O |
| |
| The following program opens the Price.Dat file created in |
| "Example 1 - Sequential File I/O" and reads the records from the |
| file, displaying the complete record on the screen if the quantity |
| for the item is less than the input amount. |
| |
| The INPUT #1 statement reads one record at a time from Price.Dat, |
| assigning the fields in the record to the variables Company$, Style$, |
| Size$, Clr$, and Qty. Since this is a sequential file, the records |
| are read in order from the first one entered to the last one entered. |
| |
| The EOF (End Of File) function tests whether the last record has been |
| read by INPUT #. If the last record has been read, EOF returns the value |
| 1 (true), and the loop for getting data ends; if the last record has not |
| been read, EOF returns the value 0 (false), and the next record is read |
| from the file. |
| |
| OPEN "Price.Dat" FOR INPUT AS #1 |
| INPUT "Display all items below what level"; Reorder |
| DO UNTIL EOF(1) |
| INPUT #1, Company$, Style$, Size$, Clr$, Qty |
| IF Qty < Reorder THEN |
| PRINT Company$, Style$, Size$, Clr$, Qty |
| END IF |
| LOOP |
| CLOSE #1 |
| END |
| |
| Example 3 - Sequential File I/O |
| |
| The WRITE # statement can be used to write records to a sequential file. |
| There is, however, another statement you can use to write sequential file |
| records: |
| |
| PRINT # |
| |
| The best way to show the difference between these two data-storage |
| statements is to examine the contents of a file created with both. The |
| following short fragment opens a file Test.Dat then places the same record |
| in it twice, once with WRITE # and once with PRINT #. After running this |
| program you can examine the contents of Test.Dat with the DOS TYPE |
| command: |
| |
| OPEN "Test.Dat" FOR OUTPUT AS #1 |
| Nm$ = "Penn, Will" |
| Dept$ = "User Education" |
| Level = 4 |
| Age = 25 |
| WRITE #1, Nm$, Dept$, Level, Age |
| PRINT #1, Nm$, Dept$, Level, Age |
| CLOSE #1 |
