IF: Start a Conditionally Executed Statement

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

• conditional_execution
  of a single statement

  IF(expression) statement

  Conditionally executes the right algned 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 ). At least an ENDIF must follow
  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	required to terminate an IF block

• a block If statement must be the first statement of 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)
• errors in the block-IF construct are color marked
• ⇾ programming - execution control