| 序号 |
名称 |
|
功能说明 & 语法 & 举例
|
| 01 |
FOR |
|
循环语句。
-----------------------------------------------------------------------------------------------
FOR variable = init, limit [, Increment] DO statement
-----------------------------------------------------------------------------------------------
FOR variable = init, limit [, Increment] DO BEGIN
statements
ENDFOR
-----------------------------------------------------------------------------------------------
◈ init：开始的数
◈ limit：结束的数
◈ Increment：增量值
◈ statement(s)：循环语句内容
|
| |
IDL> FOR i = 1, 10, 4 DO PRINT, i
1
5
9
FOR i = 1, 10, 4 DO BEGIN
PRINT, i
ENDFOR
|
| 02 |
FOREACH |
|
循环语句。
-----------------------------------------------------------------------------------------------
FOREACH Element, Variable [, Index] DO Statement
-----------------------------------------------------------------------------------------------
FOREACH Element, Variable [, Index] DO BEGIN
statements
ENDFOREACH
-----------------------------------------------------------------------------------------------
? Element：每一个元素
◈ Variable：数组变量
◈ Index：元素的索引值
◈ Statement(s)：循环语句内容
|
| |
IDL> strs = ["alex", "bn", "lee"]
IDL> FOREACH e, strs, i DO PRINT, i, "--", e
0--alex
1--bn
2--lee
strs = ["alex", "bn", "lee"]
FOREACH e, strs, i DO BEGIN
PRINT, i, "--", e
ENDFOREACH
|
| 03 |
WHILE...DO |
|
循环语句。
-----------------------------------------------------------------------------------------------
WHILE expression DO statement
-----------------------------------------------------------------------------------------------
WHILE expression DO BEGIN
statements
ENDWHILE
-----------------------------------------------------------------------------------------------
◈ expression：判断表达式
◈ statement(s)：循环语句
|
| |
IDL> i = 3
IDL> WHILE(i gt 0) DO PRINT, i--
3
2
1
i = 3
WHILE(i gt 0) DO BEGIN
PRINT, i--
ENDWHILE
|
| 04 |
IF...THEN...ELSE |
|
选择语句
-----------------------------------------------------------------------------------------------
IF expression THEN statement
-----------------------------------------------------------------------------------------------
IF expression THEN statement ELSE statement
-----------------------------------------------------------------------------------------------
IF expression THEN BEGIN
statements
ENDIF
-----------------------------------------------------------------------------------------------
IF expression THEN BEGIN
statements
ENDIF ELSE BEGIN
statements
ENDELSE
-----------------------------------------------------------------------------------------------
◈ expression：判断表达式
◈ statement(s)：语句内容
|
| |
IDL> A = 2
IDL> B = 3
IDL> IF(A EQ 2) AND (B EQ 3) THEN PRINT, 'A = ', A, STRING(13B), 'B = ', B
A = 2
B = 3
IDL> A = 2
IDL> IF(A EQ 2) THEN PRINT, 'A = ', A ELSE PRINT, 'A ≠ ', A
A = 2
A = 2
B = 3
IF(A EQ 2) AND (B EQ 3) THEN BEGIN
PRINT, 'A = ', A
PRINT, 'B = ', B
ENDIF
A = 2
IF(A EQ 2) THEN BEGIN
PRINT, 'A = ', A
ENDIF ELSE BEGIN
PRINT, 'A ≠ ', A
ENDELSE
|
| 05 |
CASE |
|
只执行符合条件的一个语句块。(多条语句需要使用 BEGIN...END）
------------------------------------------------------------
CASE expression OF
expression: statement(s)
...
expression: statement(s)
ENDCASE
------------------------------------------------------------
CASE expression OF
expression: statement(s)
...
expression: statement(s)
ELSE: satement(s)
ENDCASE
------------------------------------------------------------
CASE expression OF
expression: statement(s)
...
expression: statement(s)
ELSE: BEGIN
satement(s)
END
ENDCASE
------------------------------------------------------------
◈ expression：判断语句
◈ statement(s)：执行语句
|
| |
x=1
CASE x OF
1: PRINT, 'one'
2: PRINT, 'two'
ENDCASE
IDL Prints:
one
x=2
CASE x OF
1: PRINT, 'one'
2: PRINT, 'two'
ELSE: PRINT, 'You entered: ', x
ENDCASE
IDL Prints:
two
x=3
CASE x OF
1: PRINT, 'one'
2: PRINT, 'two'
ELSE: BEGIN
PRINT, 'You entered: ', x
PRINT, 'Please enter a value between 1 and 2'
END
ENDCASE
IDL Prints:
You entered: 3
Please enter a value between 1 and 2
|
06
|
SWITCH |
|
执行符合条件后面的所有语句块。
-----------------------------------------------------------------------------------------------
SWITCH expression OF
expression: statement(s)
...
expression: statement(s)
ENDSWITCH
-----------------------------------------------------------------------------------------------
SWITCH expression OF
expression: statement(s)
...
expression: statement(s)
ELSE: satement(s)
ENDSWITCH
-----------------------------------------------------------------------------------------------
SWITCH expression OF
expression: statement(s)
...
expression: statement(s)
ELSE: BEGIN
satement(s)
END
ENDSWITCH
-----------------------------------------------------------------------------------------------
◈ expression：判断语句
◈ statement(s)：执行语句
|
| |
x=1
SWITCH x OF
1: PRINT, 'one'
2: PRINT, 'two'
ENDSWITCH
IDL Prints:
one
two
x=2
SWITCH x OF
1: PRINT, 'one'
2: PRINT, 'two'
ELSE: PRINT, 'You entered: ', x
ENDSWITCH
IDL Prints:
two
You entered: 2
x=2
SWITCH x OF
1: PRINT, 'one'
2: PRINT, 'two'
ELSE: BEGIN
PRINT, 'You entered: ', x
PRINT, 'Please enter a value between 1 and 2'
END
ENDSWITCH
IDL Prints:
two
You entered: 2
Please enter a value between 1 and 2
|
| 07 |
REPEAT...UNTIL |
|
循环语句（与 WHILE...DO 语句类似）
-----------------------------------------------------------------------------------------------
REPEAT statement UNTIL expression
-----------------------------------------------------------------------------------------------
REPEAT BEGIN
statements
ENDREP UNTIL expression
-----------------------------------------------------------------------------------------------
◈ statement(s)：执行语句
◈ expression：判断语句
|
| |
IDL> i = 3
IDL> REPEAT PRINT, i-- UNTIL(i lt 0)
3
2
1
0
i = 3
REPEAT BEGIN
PRINT, i--
ENDREP UNTIL(i lt 0)
|
| 08 |
BEGIN...END |
|
用于显示多条语句。
-----------------------------------------------------------------------------------------------
BEGIN
statements
END | ENDIF | ENDELSE | ENDFOR | ENDFOREACH | ENDREP | ENDWHILE
-----------------------------------------------------------------------------------------------
|
| |
CASE name OF
'Moe': BEGIN
PRINT, 'Stooge'
END
ENDCASE
SWITCH name OF
'Moe': BEGIN
PRINT, 'Stooge'
END
ENDSWITCH
|
| 09 |
CONTINUE |
|
执行FOR、WHILE 或 REPEAT 循环语句中下一条循环。
|
| |
FOR I = 1,10 DO BEGIN
; If odd, start next iteration:
IF (I AND 1) THEN CONTINUE
PRINT, I
ENDFOR
IDL Prints:
2
4
6
8
10
|
| 10 |
BREAK |
|
从 FOR、WHILE、REPEAT 循环、CASE 或 SWITCH 语句中跳出。
|
| |
i = 0
PRINT, 'Initial value: ', i
WHILE (1) DO BEGIN
i = i + 1
IF (i eq 5) THEN BREAK
PRINT, 'Loop value: ', i
ENDWHILE
PRINT, 'END VALUE: ', i
IDL Prints:
Initial value: 0
Loop value: 1
Loop value: 2
Loop value: 3
Loop value: 4
END VALUE: 5
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