fortran do construct(do循环)

cite from Fortran 90 Handbook by Jeanne C. Adam,Walter S. Brainerd,Jeanne T. Martin,Brian T. Smith,Jerrold L. Wagener

有两种形式的do构造:the block DO and the nonblock DO

块化的do与非块化的do。非块化的do是为了与fortran 77兼容

块化do的一个例子是

DO I = 1, N
SUM = SUM + A (I)
END DO

非块化do的一个例子是

DO 10 I = 1, N
10 SUM = SUM + A (I)

The form of a block DO construct (R817) is:

[ do-construct-name : ] DO [ label ] [ loop-control ]
[ execution-part-construct ] ...
[ label ] end-do

where the forms of the loop control (R821) are:
[ , ] scalar-variable-name = scalar-numeric-expression , &
scalar-numeric-expression [ , scalar-numeric-expression ]
[ , ] WHILE ( scalar-logical-expression )

注:loop control即为循环控制的相关语句比如DO 10 I=1,N
and the forms of the end-do (R824) are:
END DO [ do-construct-name ]
CONTINUE

If the DO statement of a block DO construct has a construct name, the
corresponding end-do must be an END DO statement that has the same
construct name. If the DO statement of a block DO construct does not have
a construct name, the corresponding end-do must not have a construct
name.

如果block DO构造的DO语句有个构造名的话即[do-construct-name]部分，对应的end-do必须是一个有同样构造名的END DO语句。如果DO语句没有构造名，那么对应的end-do也不能有构造名。

If the DO statement does not contain a label, the corresponding end-do
must be an END DO statement. If the DO statement does contain a label,
the corresponding end-do must be identified with the same label. Note that
a block DO construct can never share its terminal statement with another
DO construct, even if it is a labeled statement. If a DO construct does share
its terminal statement with another DO construct, it is a nonblock DO
construct.

如果DO语句不包含标签的话，对应的end-do必须是一个END DO语句。如果DO语句包含标签的话，对应的end-do部分必须以相同的标签识别。block Do构造从不允许与其他的DO构造共享terminal语句（结束语句），即使是一个标签语句。如果一个DO构造与其他的DO构造共享结束语句，那么它就是一个非块化构造(nonblock construct).

The nonblock DO construct is a DO construct that either shares a terminal
statement with another DO construct, or the terminal statement is a construct
or an action statement. The nonblock DO construct always uses a label to
specify the terminal statement of the construct. 

nonblock DO构造或者与其它的DO构造共享结束语句或者结束语句是一条构造语句或者动作语句（action statement）。nonblock DO构造通常使用标签来指定该构造的结束语句。

The two forms for a nonblock
DO construct (R826) are:
action-terminated-do-construct
outer-shared-do-construct
where the form of an action terminated DO construct (R827) is:

[ do-construct-name : ] DO label [ loop-control ]
[ execution-part-construct ] ...
label action-statement

and the form of an outer shared DO construct (R830) is:

[ do-construct-name : ] DO label [ loop-control ]
[ execution-part-construct ] ...
label shared-termination-do-construct

where the forms of a shared termination DO construct (R831) are:

outer-shared-do-construct
inner-shared-do-construct

共享终止的DO构造是

外部共享do构造

内部共享do构造

注:外层是共享的do构造，内部是嵌套的共享do构造
An inner shared DO construct (R832) is:

内部的共享DO构造是
[ do-construct-name : ] DO label [ loop-control ]
[ execution-part-construct ] ...
label action-statement

integer ::i,j,kdo 2 i=1,10        x(i)=ido 2 j=1,10        y(i)=j*10do 2 k=1,10        z(k)=k*100+x(i)+y(j)2 continuedo i=1,10        write(*,*)z(i)end doend

以上代码输出结果位210,310,410,510，。。1110

三个do循环共用了label为2的语句相当于三句end do。这里相当于do循环的三重嵌套