puppybasic intro ch. 13 - working with text files

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relevant to the tutorial. for a while, it will make up  
the bulk of this section.
  
black text has been edited to be more accurate with  
regards to puppybasic.

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working with text files                                          
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                  an intro to puppybasic                                 
                                                                         
                  chapter 13: working with text files                    
                                                                         
                                                                         
                                                                         
                                                                         
                                                                         
                                                                         
                                                                         
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working with text files                                          
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working with text files is a bit different than working with binary      
files... for one, the way you open the file depends on whether you will  
be reading or writing. for this reason and a few others i prefer to      
handle text files as if they were binaries and open them for binary      
file access. you may find this is easier when you're starting out, you   
may not. often i am too lazy and instead open text files as text files.  
to print the following lines to a file:                                  
this is a line. skip the next one:                                       
                                                                         
okay, this is another line...                                            
this is, too.                                                            
                                                                         
                                                                         
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always OPEN the file:                                                    
                                                                         
OPEN "filename.txt" FOR OUTPUT AS #1                                     
                                                                         
if you do it this way it will start from scratch... that is,             
"filename.txt" will be BLANKED if it wasn't before. for this reason you  
will use APPEND for now. APPEND, instead of erasing the file, adds to    
the end of it. if you are writing to a log, this is exactly what you     
want. if you are only storing the data for a saved game file, this may   
be problematic. in that case you may prefer OPEN... FOR OUTPUT.          
regardless:                                                              
                                                                         
                                                                         
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OPEN "filename.txt" FOR APPEND AS #1                                     
                                                                         
now we'll use the PRINT statement to write our lines to the file. the    
file currently open is #1, so we'll use PRINT #1, q$                     
                                                                         
PRINT #1, "this is a line. skip the next one:"                           
PRINT #1, ""                                                             
PRINT #1, "okay, this is another line..."                                
q$ = "this is, too."                                                     
PRINT #1, q$                                                             
                                                                         
                                                                         
                                                                         
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the last line was printed differently to demonstrate again that a string 
is, after all, a string, and that you can PRINT #1, q$ as well as PRINT  
an expression in quotes. both of these are examples of valid strings.    
                                                                         
always CLOSE the file when you're done working with it:                  
CLOSE #1                                                                 
                                                                         
if you are only working with one file, or if you don't have any other    
files that you need to leave open, using CLOSE with no file numbers:     
CLOSE                                                                    
will close all the files your program has opened.                        
                                                                         
                                                                         
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now to read the file, we open it again, this time for input:             
OPEN "filename.txt" FOR INPUT AS #1                                      
                                                                         
the text file is read one line at a time. one of the most reliable ways  
to do this is to use line input from within a loop:                      
                                                                         
                                                                         
                                                                         
                                                                         
                                                                         
                                                                         
                                                                         
                                                                         
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DO: LINE INPUT #1, q$                                                    
                                                                         
PRINT q$ 'print the line to the screen                                   
                                                                         
the program has to know when to stop looping. EOF(1) is a condition that 
will be true when the end of the file is reached. it can end the LOOP    
this way:                                                                
          LOOP UNTIL EOF(1)                                              
                                                                         
you may find This LOOP superior for reading text files:                  
DO WHILE EOF(1) = 0: LINE INPUT #1, q$: LOOP 'it handles 0-length files. 
                                                                         
                                                                         
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if you only wanted to read the first line of course, the loop isn't      
needed, only line input #1, q$                                           
                                                                         
close the file when you're done with it. no files are open that need to  
stay open, so it's alright to just say:                                  
                                                                         
CLOSE                                                                    
                                                                         
                                                                         
                         -= end of chapter 13 =-                         
                                                                         
                                                                         
                                                                         
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an intro to puppybasic                                      (chapter 13) 
this content is public domain.                          
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