/* various string operations
asc(S1)          // Convert 1st character of S1 to ASCII value
chr(A)           // Convert extended ASCII value A to a 1 character string
concat(S1,S2)    // combine S1 and S2 into one long string
file_exists(S1)  // Search current and include directories for existence of file S1 (0 or 1)
str(A,L,P)       // Convert float A to string, at least L characters long,
                 // with P digits after the decimal point (if P is -1, make max)
strcmp(S1,S2)    // compare S1 to S2, return -1, 0, or +1 if S2 is <, =, > than S1
strlen(S1)       // Returns # of characters in string S1
strlwr(S1)       // Lower case of S1
substr(S1,P,L)   // Sub-string from S1, start at position P for length L
strupr(S1)       // Upper case of S1
val(S1)          // Convert string S1 to float
file_exists(S1)  // returns 1 if file S1 is found in library path
*/
/*
// some special control characters that can be used within strings
  "\a" Bell or alarm, 0x07
  "\b" Backspace, 0x08
  "\f" Form feed, 0x0C
  "\n" New line (line feed) 0x0A
  "\r" Carriage return 0x0D
  "\t" Horizontal tab 0x09
  "\uNNNN"  Unicode character code NNNN  0xNNNN  
  "\v" Vertical tab 0x0B
  "\0" Null 0x00
  "\\" Backslash 0x5C
  "\'" Single quote 0x27
  "\""  Double quote  0x22  
*/