To simulate the occurrence of an error, or to allow the user to define error codes.
ERROR integer expression
The value of integer expression must be greater than 0 and less than 255.
If the value of integer expression equals an error code already in use by GW-BASIC, the ERROR statement simulates the occurrence of that error, and the corresponding error message is printed.
A user-defined error code must use a value greater than any used by the GW- BASIC error codes. There are 76 GW-BASIC error codes at present. It is preferable to use a code number high enough to remain valid when more error codes are added to GW-BASIC.
User-defined error codes may be used in an error-trapping routine.
If an ERROR statement specifies a code for which no error message has been defined, GW-BASIC responds with the message "Unprintable Error".
Execution of an ERROR statement for which there is no error-trapping routine causes an error message to be printed and execution to halt.
The following examples simulate error 15 (the code for "String too long"):
10 S=10 20 T=5 30 ERROR S+T 40 END RUN String too long in 30
Or, in direct mode:
ERROR 15 (you type this line) String too long (GW-BASIC types this line)
The following example includes a user-defined error code message.
. . . 110 ON ERROR GOTO 400 120 INPUT "WHAT IS YOUR BET";B 130 IF B>5000 THEN ERROR 210 . . . 400 IF ERR=210 THEN PRINT "HOUSE LIMIT IS $5000" 410 IF ERL=130 THEN RESUME 120 . . .