BASIC Programming/Beginning BASIC/Control Structures/IF...THEN...ELSEIF...ELSE

The IF...THEN...ELSEIF...ELSE control statement allows identifying if a certain condition is true, and executes a block of code if it is the case.

In some implementations of BASIC (but permitted by most versions), the IF statement may need to be contained in one line. However, ELSEIF may not be available in this case, and there is no need for an explicit END IF:

This carries over into some implementations of BASIC where if the "IF...THEN" statement is followed by code on the same line then it is fully contained. That is, the compiler assumes the lines ends with "ENDIF", even if it not stated. This is important when dealing with nested "IF...THEN" clauses:

The ELSE clause, while following the "IF 2<3" statement, is associated with the "IF X<2" statement, because the "IF 2<3" statement has a PRINT statement on the same line.

Let me give some more examples of "if-then-else" programs:

Q1)Input the age of a person and check whether he/she is voter or not?

Ans1) 10 CLS 20 INPUT AGE 30 IF AGE>=18 THEN 40   PRINT "VOTER" 50 ELSE 60   PRINT "NON VOTER" 70 END IF 80 END

Q2)Input the age of a person to check if he/she is a senior citizen or not a senior citizen?

Ans2) 10 CLS 20 INPUT AGE 30 IF AGE>=60 THEN 40   PRINT "SENIOR CITIZEN"     50 ELSE 60   PRINT "NOT A SENIOR CITIZEN" 70 END IF 80 END