Problem Statement

Provide a function or mechanism to convert a provided string into URL encoding representation. In URL encoding, special characters, control characters and extended characters are converted into a percent symbol followed by a two digit hexadecimal code, So a space character encodes into %20 within the string. For the purposes of this task, every character except 0-9, A-Z and a-z requires conversion, so the following characters all require conversion by default:

The string "http://foo bar/" would be encoded as "http%3A%2F%2Ffoo%20bar%2F".

It is permissible to use an exception string (containing a set of symbols that do not need to be converted). However, this is an optional feature and is not a requirement of this task.

Let's start with the solution:

 100 URL$ = "http://foo bar/"
 110  GOSUB 140"URL ENCODE URL$ RETURNS R$
 120  PRINT R$;
 130  END
 140  LET R$ = ""
 150  LET L =  LEN (URL$)
 160  IF  NOT L THEN  RETURN
 170  LET H$ = "0123456789ABCDEF"
 180  FOR I = 1 TO L
 190      LET C$ =  MID$ (URL$,I,1)
 200      LET C =  ASC (C$)
 210      IF C <  ASC ("0") OR C >  ASC ("Z") + 32 OR C >  ASC ("9") AND C <  ASC ("A") OR C >  ASC ("Z") AND C <  ASC ("A") + 32 THEN H =  INT (C / 16):C$ = "%" +  MID$ (H$,H + 1,1) +  MID$ (H$,C - H * 16 + 1,1)
 220      LET R$ = R$ + C$
 230  NEXT I
 240  RETURN