Q(uick)BASIC Function: INSTR

Quick View

INSTR

A string processing function that returns the character position of the first occurrence of a string in another string

Worth knowing

Useful and cross-version information about the programming environments of QBasic and QuickBasic.

Syntax

INSTR([start%,]stringexpression1$,stringexpression2$)

Description/Parameter(s)

start%	Sets the character position where the search begins. If start% is omitted, INSTR starts at position 1.
stringexpression1$	The string to search.
stringexpression2$	The string to look for.

Example

a$ = "Microsoft QBasic"
PRINT "String position ="; INSTR(1, a$, "QBasic")

Syntax

INSTR([start,]stringexpression1,stringexpression2)

Description/Parameter(s)

Argument	Description
start	An optional offset that sets the position for starting the search; start must be in the range 1-32,767. If start is not given, the INSTR function begins the search at the first character of stringexpression1.
stringexpression1	The string being searched.
stringexpression2	The string to look for.

The arguments stringexpression1 and stringexpression2 can be string variables, string expressions, or string literals.

The value returned by INSTR depends on the following conditions:

Condition	Value Returned
stringexpression2 found in stringexpression1	The position at which the match is found
start greater than length of stringexpression1	0
stringexpression1 is null string	0
stringexpression2 cannot be found	0
stringexpression2 is null string	start (if given); otherwise, 1

Use the LEN function to find the length of stringexpression1.

Example

This example uses INSTR and UCASE$ to determine a person's sex from their courtesy title (Mr., Mrs., or Ms.).

' Get a name.
CLS    ' Clear screen
DO
   INPUT "Enter name including courtesy title (Mr., Mrs., or Ms.): ", Nm$
LOOP UNTIL LEN(Nm$) >= 3

' Convert lowercase letters to uppercase.
Nm$ = UCASE$(Nm$)
' Look for MS, MRS, or MR to set Sex$.
IF INSTR(Nm$, "MS") > 0 OR INSTR(Nm$, "MRS") > 0 THEN
    Sex$ = "F"
ELSEIF INSTR(Nm$, "MR") > 0 THEN
    Sex$ = "M"
ELSE
    ' Can't determine sex, query user.
    DO
        INPUT "Enter sex (M/F): ", Sex$
        Sex$ = UCASE$(Sex$)
    LOOP WHILE Sex$ <> "M" AND Sex$ <> "F"
END IF
' Print result
PRINT "Sex is "; Sex$

Sample Output:

Enter name: Ms. Elspeth Brandtkeep Sex is F Enter name: Dr. Richard Science Enter sex (M/F): M Sex is M

Syntax

INSTR([start%,]stringexpression1$,stringexpression2$)

Description/Parameter(s)

The arguments stringexpression1$ and stringexpression2$ can be string variables, string expressions, or string literals.

Usage Notes

The value returned by INSTR depends on the following conditions:

Condition	Value returned
stringexpression2$ found in stringexpression1$	The position at which the match is found
start% greater than length of stringexpression1$	0
stringexpression1$ is null string	0
stringexpression2$ cannot be found	0
stringexpression2$ is null string	start% (if given); otherwise, 1

Use the LEN function to find the length of stringexpression1$.

Example

This example uses INSTR and UCASE$ to determine a person's gender from their courtesy title (Mr., Mrs., or Ms.).

'Get a name.
CLS    'Clear screen.
DO
   INPUT "Enter name including courtesy title (Mr., Mrs., or Ms.): ", Nm$
LOOP UNTIL LEN(Nm$) >= 3
 
'Convert lowercase letters to uppercase.
Nm$ = UCASE$(Nm$)
'Look for MS, MRS, or MR to set Sex$.
IF INSTR(Nm$, "MS") > 0 OR INSTR(Nm$, "MRS") > 0 THEN
    Sex$ = "F"
ELSEIF INSTR(Nm$, "MR") > 0 THEN
    Sex$ = "M"
ELSE
    'Can't determine sex, query user.
    DO
  INPUT "Enter sex (M/F): ", Sex$
  Sex$ = UCASE$(Sex$)
    LOOP WHILE Sex$ <> "M" AND Sex$ <> "F"
END IF
'Print result.
PRINT "Sex is "; Sex$

Sample Output:

Enter name: Ms. Elspeth Brandtkeep Sex is F Enter name: Dr. Richard Science Enter sex (M/F): M Sex is M