为什么我们使用“End If”语句？

Question

为什么我们在这个程序中写END IF 语句？不写它，我们可以很容易地得到我们的结果。有没有例子可以解释一下END IF语句的用法？

我试过这个：

INPUT X
IF X>10 THEN PRINT "X IS GREATER THAN 10" ELSE PRINT "X IS NOT GREATER THAN 10"
END

那么我也得到了预期的结果。

真正的代码是：

INPUT X
IF X>10 THEN 
    PRINT "X IS GREATER THAN 10"
ELSE
    PRINT "X IS NOT GREATER THAN 10"
END IF
END

预期和期望
例如：
当X=5 时，输出将是“X IS NOT GREATER THAN 10”。

Answer 1

需要END IF 来指示以多行编写的IF, ELSE IF, ELSE 结构的结尾。如果没有END IF（缺少会导致错误），那么IF, ELSE IF, ELSE 结构下的语句将被视为IF, ELSE IF, ELSE 结构的一部分，直到出现END IF。如果没有END IF，那么IF, ELSE IF, ELSE结构的使用将被限制为只能在程序结束时使用

考虑这样一种情况，如果条件为真，您希望运行 100 行特定的行，如果条件为假，则需要运行 100 行其他行，并且必须始终在 IF-ELSE 结构之后执行另外 100 行。现在显然你不能将所有这 200 条IF ELSE 相关的行写在一行中。如果没有END IF，那么就无法运行接下来的 100 行。

---

END IF对于一行写的IF, ELSE IF, ELSE语句无效。下一行中的任何语句都将被视为不属于IF, ELSE IF, ELSE 结构。并非总是可以在一行中编写所有必需的功能。所以，它只能在基于某些条件触发一个可以写在一行中的小功能时使用。所以这就是这种单线方法的缺点。

Answer 2

多个缩进的 if/then/else 语句可以比单行语句更容易组合成一个结构，例如：

INPUT X
IF X > 10 THEN
    PRINT "X is greater than 10."
ELSE
    IF X < 10 THEN
        PRINT "X is less than 10."
    ELSE
        PRINT "X is equal to 10."
    END IF
END IF

等同于：

INPUT X
IF X > 10 THEN PRINT "X is greater than 10." ELSE IF X < 10 THEN PRINT "X is less than 10." ELSE PRINT "X is equal to 10."

如果/那么在一行中测试 3 个数字的值是非常困难的，例如：

INPUT X, Y, Z
IF X = 0 AND Y = 0 AND Z = 0 THEN PRINT "All zero." ELSE IF X = 0 AND Y <> 0 AND Z = 0 THEN PRINT "X and Z zero." ELSE IF X <> 0 AND Y = 0 AND Z = 0 THEN PRINT "Y and Z zero." ELSE IF X = 0 AND Y = 0 AND Z <> 0 THEN PRINT "X and Y zero." ELSE IF X <> 0 AND Y <> 0 AND Z = 0 THEN PRINT "X and Y non-zero." ELSE IF X <> 0 AND Y = 0 AND Z <> 0 THEN PRINT "X and Z non-zero." ELSE IF X = 0 AND Y <> 0 AND Z <> 0 THEN PRINT "Y and Z non-zero." ELSE PRINT "All non-zero."

Answer 3

确定3个输入值的另一个例子：

COLOR 15
DO
    PRINT "Enter values(y/n)";: INPUT x$
    IF LCASE$(x$) = "n" THEN END
    PRINT "Enter X,Y,Z";: INPUT X, Y, Z
    GOSUB Calculate
LOOP
END
Calculate:
SELECT CASE X
    CASE IS > 0
        SELECT CASE Y
            CASE IS > 0
                SELECT CASE Z
                    CASE IS > 0
                        PRINT "X is positive, Y is positive, Z is positive."
                    CASE IS < 0
                        PRINT "X is positive, Y is positive, Z is negative."
                    CASE ELSE
                        PRINT "X is positive, Y is positive, Z is zero."
                END SELECT
            CASE IS < 0
                SELECT CASE Z
                    CASE IS > 0
                        PRINT "X is positive, Y is negative, Z is positive."
                    CASE IS < 0
                        PRINT "X is positive, Y is negative, Z is negative."
                    CASE ELSE
                        PRINT "X is positive, Y is negative, Z is zero."
                END SELECT
            CASE ELSE
                SELECT CASE Z
                    CASE IS > 0
                        PRINT "X is positive, Y is zero, Z is positive."
                    CASE IS < 0
                        PRINT "X is positive, Y is zero, Z is negative."
                    CASE ELSE
                        PRINT "X is positive, Y is zero, Z is zero."
                END SELECT
        END SELECT
    CASE IS < 0
        SELECT CASE Y
            CASE IS > 0
                SELECT CASE Z
                    CASE IS > 0
                        PRINT "X is negative, Y is positive, Z is positive."
                    CASE IS < 0
                        PRINT "X is negative, Y is positive, Z is negative."
                    CASE ELSE
                        PRINT "X is negative, Y is positive, Z is zero."
                END SELECT
            CASE IS < 0
                SELECT CASE Z
                    CASE IS > 0
                        PRINT "X is negative, Y is negative, Z is positive."
                    CASE IS < 0
                        PRINT "X is negative, Y is negative, Z is negative."
                    CASE ELSE
                        PRINT "X is negative, Y is negative, Z is zero."
                END SELECT
            CASE ELSE
                SELECT CASE Z
                    CASE IS > 0
                        PRINT "X is negative, Y is zero, Z is positive."
                    CASE IS < 0
                        PRINT "X is negative, Y is zero, Z is negative."
                    CASE ELSE
                        PRINT "X is negative, Y is zero, Z is zero."
                END SELECT
        END SELECT
    CASE ELSE
        SELECT CASE Y
            CASE IS > 0
                SELECT CASE Z
                    CASE IS > 0
                        PRINT "X is zero, Y is positive, Z is positive."
                    CASE IS < 0
                        PRINT "X is zero, Y is positive, Z is negative."
                     CASE ELSE
                        PRINT "X is zero, Y is positive, Z is zero."
                END SELECT
            CASE IS < 0
                SELECT CASE Z
                    CASE IS > 0
                        PRINT "X is zero, Y is negative, Z is positive."
                    CASE IS < 0
                        PRINT "X is zero, Y is negative, Z is negative."
                    CASE ELSE
                        PRINT "X is zero, Y is negative, Z is zero."
                 END SELECT
            CASE ELSE
                SELECT CASE Z
                     CASE IS > 0
                        PRINT "X is zero, Y is zero, Z is positive."
                    CASE IS < 0
                        PRINT "X is zero, Y is zero, Z is negative."
                    CASE ELSE
                         PRINT "X is zero, Y is zero, Z is zero."
                END SELECT
         END SELECT
END SELECT
RETURN

Answer 4

另一种方法是使用选择案例：

INPUT X
SELECT CASE X
    CASE IS > 10
        PRINT "X is greater than 10."
    CASE IS < 10
        PRINT "X is less than 10."
    CASE ELSE
        PRINT "X is equal to 10."
END SELECT