Commodore Plus 4 - Page 62

50 The BASIC Language
clause is ignored and execution passes to the next line in the program or to the
ELSE clause if one is present.
The GOTO clause is like a GOTO command: it tells the computer to go straight
to a specified line number and resume execution there. The line number can be
anywhere in the program.
IF ... GOTO ... ELSE is a limited variation of IF ... THEN ... ELSE. Use
IF... GOTO... ELSE instead of IF... THEN... ELSE when the THEN clause
would contain a GOTO command anyway.
Parameters: true-false condition GOTO line number : ELSE clause
1. The conditions in the IF command can use comparison operators (=, <, >,
<>, <=, >=) to compare values. The values can be any of the following:
• Numbers or text strings
• Any type of variable
• Variables on both sides of the comparison operator
• Mathematical formulas
2. The line number after GOTO tells the computer where to go when the IF
condition(s) is (are) true.
3. The ELSE clause contains instructions that are followed only when the IF
condition(s) is (are) false. The ELSE clause is always optional. It must be
separated from the rest of the command by a colon.
Example: 10 IITRJT X Line 20 compares the value input for X to 0.
SO IF X <= 0 GOTO 10 The GOTO command executes only when it is
30 PRINT X true that X is less than or equals 0.
IF ... THEN ... ELSE Abbrs. if/tH/eL
IF logical value THEN commands : ELSE commands
IF is a compound conditional statement that checks the status of a condition in
the command and then chooses one of two courses of action.
One of the two IF command options is stated in the THEN clause. The other
option can be stated in an ELSE clause. If no ELSE clause is present, execution
continues with the next line in the program when the condition is false.
The status of the IF command condition determines whether the THEN clause
or the alternative is to be executed. THEN is executed when the IF condition is
true, or met; ELSE is executed when the IF condition is false, or not met. The
computer executes either the THEN clause or the ELSE clause, but never both.