IF

From C64-Wiki

BASIC keyword
Keyword:	IF
Abbreviation:	-
Type:	Command
Token code:	-/$-
Handling routine in BASIC ROM:	-–- $-–-
List of all BASIC keywords

Remark: This article describes the BASIC-Command IF in BASIC V2 at the Commodore 64.

Typ: Command
General Programming-Syntax: IF <equation> THEN <linenumber> 
                               or IF <equation> GOTO <linenumber> 
                               or IF <equation> THEN <command>

The BASIC-Command IF is used together with the BASIC-Command THEN or with the BASIC-Command GOTO by equations. When the equations is right or true, the BASIC-Commands after THEN or the GOTO-Command is running. By a wrong equation the BASIC interpreter will be ignore the following BASIC commands in this line.

For the equantion will be needed this relational operators:

• = equal
• <> unequal
• < less than
• > greater
• <= less-equal
• >= greater-equal

Furthermore can be used logical operators like AND, OR or NOT and by using more than one equations for combining or seperating, can be used brackets ().

[edit] Examples

10 PRINTCHR$(147);
20 INPUT "2 numbers, please: ";A$, B$
30 IF A$="" OR B$="" THEN 20
40 A=VAL(A$): B=VAL(B$)
50 IF A>0 THEN PRINT "A is posotiv and ";
51 IF A<0 THEN PRINT "A is negativ and ";
52 IF A=B THEN PRINT "A is equal B ";
53 IF A<>B THEN PRINT "A is unequal B ";
54 IF NOT A AND NOT B THEN PRINT ", no number value is -1";
55 IF A=64 AND B=64 THEN PRINT " !!! BINGO !!!": GOTO 58
56 IF A=B AND A=0 GOTO 58
57 IF (A AND B=0) OR (NOT B AND A=0) THEN END
58 FOR X=0 TO 3000: NEXT
59 GOTO 10