循环类型

循环类型	说明
while	当给定条件为真时，重复一个语句或一组语句。在执行循环体之前测试条件
do	do语句对于将特定任务重复特定次数很有用
nested（嵌套）	可以在任何另一个while或do循环中使用一个或多个循环

while

while <logical expression>
<statement block>.
endwhile

report ys_sep_15.
data: a type i.
a=0.
while a<>8.
  write: / 'this is the line:', a.
  a=a+1.
endwhile.

This is the line: 0 
This is the line: 1 
This is the line: 2 
This is the line: 3 
This is the line: 4 
This is the line: 5 
This is the line: 6 
This is the line: 7

DO

do [n times].
<statement block>.
enddo.

report yh_sep_15.
do 5 times.
write: / 'hello'.
enddo.

Hello 
Hello 
Hello 
Hello 
Hello 

nested(嵌套)

do [n times].
<statement block n>.
  do [m times].
  <statement block m>.
  enddo.
enddo.

report ys_sep_15.
data: a1 type i, b1 type i.
a1 = 0.
b1 = 0.
do 2 times.
a1 = a1 + 1.
write: / 'outer', a1.

do 3 times.
b1 = b1 + 1.
write: / 'inner', b1.
enddo.
enddo.

Outer   1 
Inner   1 
Inner   2 
Inner   3 
Outer   2 
Inner   4
Inner   5 
Inner   6

---

循环控制语句

控制语句	说明
continue	导致循环跳过其身体的剩余部分，并开始下一个循环传递
check	如果条件为假，则在check之后的剩余语句被忽略，并且系统开始下一循环通过
exit	完全终止循环，并将执行转移到循环后立即执行的语句

continue

report yh_sep_15.
do 5 times.
if sy-index = 3.

continue.

endif.
write / sy-index.
enddo.

1
2
4
5

check

report th_sep_15.
do 5 times.
check sy-index detween 3 and 4.
write / sy-index.
enddo.

3
4

exit

report yh_sep_15.
do 5 times.
if sy-index = 3.
exit.
endif.
write / sy-index.
enddo.

1
2