INSTR()

Description

Returns position of string2 within first string, string1. Begins search at starting parameter, if supplied.

Syntax

1. instr(string1, string2, [starting])

Hints

If the second string is found more that once, only the position of the first found (leftmost) will be returned.

But you can continue using returned result for starting parameter, see second example.

INSTR returns 0 if the string is not found (starting from the beginning or supplied starting parameter).

There are three main uses of INSTR function:

• checking if string2 exists in string1 (first example)
• using returned position for operations on string1 (Replace$() function)
• using returned position for it's numerical value (hex2Dec() function)

Example

' User chooses...
[start]
    input "Chose 1 or 2 "; choice
    choice$ = str$(choice)
    if instr(choice$, "1") > 0 then
        print "You chose 1."
        print "You are correct!"
    else
        print "Sorry. Wrong choice."
    end if

    print
    input "Do you want to play again, yes or no? "; yesno$
    if instr("yes", lower$(yesno$)) > 0 then
        print "You answered yes."
        print "Returning to start now."
        goto [start]
    else
        print "OK. You don't want to continue. Bye."
    end if

    end

'Example for using Instr for finding all instances of a word in a text

duchessQuote$ = "Be what you would seem to be -- or, if you'd like it put more simply -- " +chr$(13) _
+"Never imagine yourself not to be otherwise than what it might appear to others " +chr$(13) _
+"that what you were or might have been was not otherwise " +chr$(13) _
+"than what you had been would have appeared to them to be otherwise."  +chr$(13) _

print duchessQuote$
print "finding all 'you' in text:"
i=0
do
    i = instr(duchessQuote$, "you", i+1)
    if i<>0 then print "Found at position ";i
loop until i=0
print "That's all"

Useful Procedures

'finds all occurences of old$ in string$ (using instr()) and replaces them with new$

FUNCTION Replace$( string$, old$, new$)
  pos = 1
  WHILE pos
    prevpos = pos
    pos = instr(string$, old$, pos)
    IF pos THEN
      Replace$ = Replace$ + mid$(string$, prevpos, pos - prevpos) + new$
      pos = pos + len(old$)
    END IF
  WEND
  Replace$ = Replace$ + Mid$( string$,prevpos)
END FUNCTION

'Converts HEX string to (decimal) number. So, "FF"->255
function hex2Dec(s$)
    hex2Dec = 0
    For I = 1 To Len(s$)
        c$ = upper$(Mid$(s$, I, 1))
        If InStr("0123456789ABCDEF", c$) = 0 Then exit function    'like VAL, it stops on first non-valid symbol
        hex2Dec = hex2Dec * 16 + InStr("0123456789ABCDEF", c$) - 1
    Next I
End Function

' Converts hexadecimal number (string) to decimal number.
' Processes the hex number from right to left, so any hex notation is allowed.
' Examples: &hFF = 0xFF = FF

FUNCTION JBhexdec(HexString$)
    ValidHex$ = "0123456789ABCDEF"
    power = 0
    JBhexdec = 0

    for i = len(HexString$) to 1 step -1
        HexDigit$ = upper$(mid$(HexString$, i, 1))

        ' exit at first non-hexadecimal digit
        if instr(ValidHex$, HexDigit$) = 0 then exit for

        JBhexdec = JBhexdec + (instr(ValidHex$, HexDigit$) - 1) * 16 ^ power

        power = power + 1
    next
END FUNCTION