GW-BASIC中的嵌套IF...THEN...ELSE

Question

我使用下面的代码块来测试gw-basic程序中的一些条件。

IF Average >= 80 AND Average <= 100 THEN Grade$ = "A"
IF Average >= 70 AND Average <= 79 THEN Grade$ = "B"
IF Average >= 60 AND Average <= 69 THEN Grade$ = "C"
IF Average >= 50 AND Average <= 59 THEN Grade$ = "D"
IF Average >= 40 AND Average <= 49 THEN Grade$ = "E" ELSE Grade$ = "F"  
PRINT "Average is: ", Average
PRINT "Grade is: ", Grade$

它总是打印Grade is: F，不管±verage的值是什么。

这个gw-basic程序中的错误是什么？

Answer 1

如果平均>=为40，平均<=为49，则等级$= "E“否则等级$= "F”

因为这行IF THEN ELSE总是会给IF THEN$赋值(不管Average的内容是什么)，所以前面的所有值都没有多大价值。

然而，解决方案是非常非常简单的。不要使用ELSE子句，一开始就给等级$一个默认值"F“。这样，只有当所有这些条件的计算结果都为false时，程序才会返回"Grade is: F“。

Grade$ = "F"
IF Average >= 80 AND Average <= 100 THEN Grade$ = "A"
IF Average >= 70 AND Average <= 79 THEN Grade$ = "B"
IF Average >= 60 AND Average <= 69 THEN Grade$ = "C"
IF Average >= 50 AND Average <= 59 THEN Grade$ = "D"
IF Average >= 40 AND Average <= 49 THEN Grade$ = "E"
PRINT "Average is: ", Average
PRINT "Grade is: ", Grade$

Answer 2

假设打印平均行是行号70，那么在除ELSE行之外的每一行之后写入GOTO 70。如果有效的话，试试吧。