IF THEN statement is a decision making statement.it is used to excute or to ignor a statement or a set of statements after testing a condition.
IF ..THEN..ELSE Statement is used To make a decision regarding program flow based on the result returned by an expression. If the result of expression is nonzero (logical true), the THEN or GOTO line number is executed
If the result of expression is zero (false), the THEN or GOTO line number is ignored and the ELSE line number, if present, is executed. Otherwise, execution continues with the next executable statement. A comma is allowed before THEN and ELSE. Syntax:
IF expression[,] THEN statement(s)[,][ELSE statement(s)]
IF expression[,] GOTO line number[[,] ELSE statement(s)]