Guidance
指路人
g.yi.org
software / RapidQ / RQ Doc / html / conditions.html

Register 
新用户注册
Search 搜索
首页 
Home Home
Software
Upload

  
Appendix C: Conditions
Rapid-Q Documentation by William Yu (c)1999 Appendix C: Conditions


Introduction to Condition Statements

Conditional statements offer the ability to execute code for which the condition is satisfied. This is probably one of the first things you learn in programming, besides the usual.

IF .. THEN .. ELSE
There are 2 ways to use IF .. THEN .. ELSE. You can place your statement on one single line like so:
    IF I > 100 THEN PRINT "I is greater than 100"
Or split it up like so:
    IF I > 100 THEN
      PRINT "I is greater than 100"
    END IF
As you can see, I > 100 is a condition, as long as this is satisfied, the code gets executed, if not then that piece of code is skipped. A condition is satisfied whenever the expression evaluates to any non-zero number. Which also means that this is valid:
   I = 100
   IF I THEN
     PRINT "Condition satisfied"
   ELSE
     PRINT "Condition is not satisfied"
   END IF
Use ELSEIF whenever you have multiple conditions that you want satisfied:
   IF I > 10 AND I < 20 THEN
      '' do stuff
   ELSEIF I > 55 THEN
      '' do stuff
   ELSE
      '' do stuff
   END IF
Sometimes it helps to use SELECT CASE instead of all these ELSEIFs, which we'll cover next.

SELECT CASE .. END SELECT
Select cases are usually implemented when you have a lot of conditions that you want to test for. It's really not useful if you only have 2 or 3 conditions, but no one's stopping you from using it. There are no special cases in using SELECT CASEs in Rapid-Q, so everything you learned in QBasic, can be implemented here as well.
    SELECT CASE Expression
      CASE 1
        '' Do stuff
      CASE 5
        '' Do stuff
      CASE ELSE
        '' No conditions satisfied, do stuff
    END SELECT
It probably involves less typing, but there are many other useful purposes, for example, range testing becomes so much easier:
    SELECT CASE Expression
      CASE 1 TO 4, 10 TO 20
        '' Do stuff
      CASE 100 TO 150
        '' Do stuff
      CASE IS > 200
        '' Do stuff
    END SELECT
As you can see, you can have multiple test conditions by separating each with a comma. I think you can figure out how the IS keyword is used.


<- User Defined Types Contents Loops ->
掌柜推荐
 
 
 
 
 
 
 
 
 
 
 
 
© Thu 2017-9-21  Guidance Laboratory Inc.
Email:webmaster1g.yi.org Hits:0 Last modified:2015-12-25 19:42:23