puppybasic intro ch. 08 - strings part ii

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strings part ii:  searching and manipulation                              
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                  an intro to puppybasic                                 
                                                                         
                  chapter 8: strings part ii                              
                                                                         
                                                                         
                                                                         
                                                                         
                                                                         
                                                                         
                                                                         
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strings part ii:  searching and manipulation                              
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although you could find a better routine to do the same thing, INSTR is  
a very fast and simple way to see if and when a string exists as part of 
a larger string: for instance:                                           
                                                                         
suppose q$ is storing the string:                                        
"the quick brown fox jumped, and stuff."                                 
                                                                         
and you want to know if the string (let's pretend you don't know what q$ 
is; maybe it's from a file or the keyboard.) contains the word "fox" so  
you code:                                                                
                                                                         
                                                                         
                                                                         
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strings part ii:  searching and manipulation                              
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n = INSTR(q$, "fox")                                                     
                                                                         
n will be equal to the number of letters, numbers, and punctuation that  
you have to read before you've started reading "fox"... in this case,    
the "f" in "fox" is the 17th byte in q$, so INSTR will set n to 17. if   
the string "fox" is not found in the string that q$ is storing, n will   
be set to 0.                                                             
                 1                                                       
 123456789012345 7 90123456789012345678                                  
"the quick brown fox jumped, and stuff."                                 
                                                                         
                                                                         
                                                                         
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strings part ii:  searching and manipulation                              
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SPACE$                                                                   
                                                                         
is really, really easy to use. SPACE$(n) is a string of ascii 32 (space) 
that is n bytes long. q$=q$+SPACE$(10) will add 10 spaces to the end of  
q$.                                                                      
                                                                         
LEFT$ and RIGHT$                                                         
                                                                         
are not as powerful or complete as MID$ but are slightly easier to use.  
skipping straight to examples, LEFT$("Seventy",5) is "Seven" and         
RIGHT$("elephant",3) is "ant". MID$ is similar:                          
                                                                         
                                                                         
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strings part ii:  searching and manipulation                              
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the syntax for the MID$ function is:                                     
                                                                         
MID$(q$, whichbytetostartat, howmanybytes)                               
                                                                         
so n$=MID$("hello", 2, 4) would set n$ to "ello" and                     
n$=MID$("yeah, or... something", 14, 2) would set n$ to "om".            
                                                                         
there is a MID$ statement as well, which works the same way, except      
instead of reading a string it will rewrite it:                          
                                                                         
                                                                         
                                                                         
                                                                         
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strings part ii:  searching and manipulation                              
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y$="yeah, or... something"                                               
n$=SPACE$(2)+"no"                                                        
                                                                         
MID$(y$, 13, 4)=n$                                                       
                                                                         
will store "yeah, or...   nothing" in y$. the 4-byte "some" has been     
replaced with 2 spaces and "no", changing "something" to "  nothing".    
whoosh!                                                                  
                                                                         
                                                                         
                                                                         
                                                                         
                                                                         
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strings part ii:  searching and manipulation                              
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if you do not like the MID$ statement for rewriting, it is totally       
possible to avoid it entirely using only the MID$ "reading" function     
and concatonization of strings.                                          
                                                                         
there are times (especially with code like the first menu routine,       
earlier) when your variable will have leading or trailing spaces that    
you don't want. when you use STR$(n) to convert a numeric variable to a  
string for instance, it will contain a leading space (if it is at least  
zero) for a plus sign, even though the plus sign will never show. if the 
number drops below zero, a negative sign will show, but otherwise, you   
may be stuck with a space you don't want, like this: " 55".              
                                                                         
                                                                         
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strings part ii:  searching and manipulation                              
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LTRIM$(STR$(n))                                                          
                                                                         
will remove the leading spaces from a number, and LTRIM$(RTRIM$(q$))     
will remove the spaces from both ends of any string. this is not only    
useful when changing numbers to strings, but also when accepting         
keyboard input or data from files.                                       
                                                                         
                                                                         
                         -= end of chapter 8 =-                          
                                                                         
                                                                         
                                                                         
                                                                         
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an intro to puppybasic                                       (chapter 8) 
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