Commodore Plus 4 - Page 180

168 Some Programming Techniques
40 IP FE>0 THEN Ft(X)=LEFT$(L$(X),FE-1):
L$(X)=RIGHT$(L$(X),LEN(Lf(X))-FE)
50 PRINT "LAST NAME: ";L$(X);:
IF LEN(F$(X))>0 THEN PRINT " FIRST NAME: ";Ff (X);
60 PRINT:NEXT
LEN can be used to figure a parameter in a LEFTS, RIGHTS, or MID$
function. For example, in the following program, the starting position in the
MIDS function in line 30 uses the LENgth of S$:
10 INPUT "MONTH/DAY/YEAR"; S$
30 PRINT"THIS IS DAY ";MID$(S$,LEN(S$)-4,2);" OF MONTH ";
LEFT$(S$,2)
RUN
MONTH/DAY/YEAR? 12/25/84
THIS IS DAY 25 OF MONTH 12
You can also use the string functions to search input for characters that are not
acceptable for your application. For example, suppose an error will occur in your
program if information being input contains numbers. You can use the string
functions to search each piece of input for a number.
10 INPUT "FULL NAME"; S$
20 FOR 1=48 TO 57
30 Y = INSTR(S#,CHR$(I))
40 IF Y>0 THEN PRINT "ILLEGAL INPUT; CHARACTER" ;Y;
"IS A NUMBER"
50 NEXT
The INSTR (IN STRing) function finds the starting position of a string
embedded within another string. INSTR searches a text string from left to right
and returns a number that tells you the character position of the first character in
the sought string.
Like the LEN function, INSTR is a numeric function, which means it returns a
number, not a text string. Also like LEN, INSTR works only on a text string
expression, not on a number.
Converting Strings and Numeric Values: STRl and VAL
The STRS function converts numeric values into text strings. You would use this
conversion when you want to use a string function to search the number. There
are no numeric functions comparable to LEFTS, RIGHTS, MIDS, and LEN. So