【217】◀▶ IDL 控制语句说明

参考：Statements Routines —— 控制语句关键字

---

01		FOR	循环语句。
02		FOREACH	循环语句。
03		WHILE...DO	循环语句。
04		IF...THEN...ELSE	选择语句。
05		CASE	只执行符合条件的一个语句块。
06		SWITCH	执行符合条件后面的所有语句块。
07		REPEAT...UNTIL	循环语句。
08		BEGIN...END	用于显示多条语句。
09		CONTINUE	执行循环语句中的下一条循环。
10		BREAK	从循环、CASE 或 SWITCH 语句中跳出。

---

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