IF: start a conditionally executed statement (F)

• Conditionally executes a group of statements, depending on the value of an expression

• conditional execution

  of a single statement

  IF(expression) statement

  Conditionally executes one statement if expression evaluates to non-zero IF(INDEX(txt, " ") > 0 ) WRITE() txt ! write if txt is not blank

• conditionally execute blocks of statements

  IF (expr1) THEN	1st statement of an IF construct IF( x ) THEN ! if x is true ( if it is not 0 )
  true block	executed if expr1 is non-zero a = a / x
  ELSEIF (expr2) THEN	ELSEIF( (a < x) * OK ) THEN ! if a is less than x AND OK is not zero
  elseif block	executed if expr2 is non-zero a = a ** x ! same as a = a ^ x
  ELSE
  else block	executed if expr1 == expr2 == 0 (false) a = a + 1 x = 2 * x
  ENDIF	terminates an IF construct

• a block If statement must be the first statement on a line. The block IF must end with an ENDIF statement.
• ELSE and ELSEIF are both optional. There can be multiple ELSEIF statements in a block IF, but none can appear after the ELSE
• block IF statements can be nested (contained within one another)
• ⇒ Programming - execution control