Commodore Plus 4 - Page 179

Using tlie String Functions 167
The Substring Functions: LEFTf, RIGHTS, and MIDI
The functions LEFTS, RIGHTS, and MIDS can be used to form a substring of a
text string. Use these functions to check input or to assign part of a string to a
string variable. These functions are frequently used in conditional statements.
For example, you can use LEFTS to check the first letter of the input.
Each of these functions can return up to 255 characters, which is the maximum
length of a string. If the substring is longer than the master string, the computer
returns the entire master string (starting from the function starting point).
The parameters for each function are enclosed in parentheses. The first
parameter for each of these functions is the master string, which can be any legal
string. The second parameter in the LEFTS and RIGHTS functions is the length
of the substring. The second MIDS parameter is the starting location for the
substring. The third MIDS parameter is the substring length.
The LEFTS substring begins at the leftmost character in the master string and
continues for the specified number of characters. The RIGHTS substring has the
specified length and ends at the rightmost character in the master string. The
MIDS substring can begin at any character position in the master string and
continues for the specified number of characters.
Examples: 10Y$ = "REDWHITEBLUE"
20 X$ = MID$(Y$,4,5) X$ is the word WHITE.
PRINT LEFT$("RED",4) The string contains only
RED three characters, so
only three are printed.
10 INPUT "DO YOU WANT TO CONTINUE"; A$ Searches text string AS,
20 IP LEFT$(A$,1>"Y" THEN GOSUB 70: input in line 10, for
ELSE END the string Y.
Finding the Length of a String: the LEN(X$) Function
LEN counts the total number of characters in a text string. Any text string can be
counted. Blank spaces and punctuation marks count as characters in the string.
For example "HO HO!" has six characters. You can use any string expression,
even a text-string array element, as the LEN parameter.
The following example uses array elements as string function parameters:
5 DIM P$(49),L$(49)
10 F0RX=0T0 49
20 INPUT "NEXT NAME";L$(X)
30 FE=INSTR(L$(X)," ")