📅 最后修改于: 2020-11-22 16:49:38 🧑 作者: Mango
条件语句用于根据程序员指定的某些条件来更改执行流程。条件语句将始终为true或false。在IF，Evaluate和Perform语句中使用条件。不同类型的条件如下-
IF语句检查条件。如果条件为真，则执行IF块；否则，执行IF块。如果条件为假，则执行ELSE块。
END-IF用于结束IF块。要结束IF块，可以使用句点代替END-IF。但是，最好将END-IF用于多个IF块。
嵌套IF -IF块出现在另一个IF块中。嵌套IF语句的深度没有限制。
以下是IF条件语句的语法-
IF [condition] THEN
[COBOL statements]
ELSE
[COBOL statements]
END-IF.
例
IDENTIFICATION DIVISION.
PROGRAM-ID. HELLO.
DATA DIVISION.
WORKING-STORAGE SECTION.
01 WS-NUM1 PIC 9(9).
01 WS-NUM2 PIC 9(9).
01 WS-NUM3 PIC 9(5).
01 WS-NUM4 PIC 9(6).
PROCEDURE DIVISION.
A000-FIRST-PARA.
MOVE 25 TO WS-NUM1 WS-NUM3.
MOVE 15 TO WS-NUM2 WS-NUM4.
IF WS-NUM1 > WS-NUM2 THEN
DISPLAY 'IN LOOP 1 - IF BLOCK'
IF WS-NUM3 = WS-NUM4 THEN
DISPLAY 'IN LOOP 2 - IF BLOCK'
ELSE
DISPLAY 'IN LOOP 2 - ELSE BLOCK'
END-IF
ELSE
DISPLAY 'IN LOOP 1 - ELSE BLOCK'
END-IF.
STOP RUN.
JCL执行上述COBOL程序-
//SAMPLE JOB(TESTJCL,XXXXXX),CLASS = A,MSGCLASS = C
//STEP1 EXEC PGM = HELLO
当您编译并执行上述程序时，它将产生以下结果-
IN LOOP 1 - IF BLOCK
IN LOOP 2 - ELSE BLOCK
关系条件比较两个操作数，两个操作数都可以是标识符，字面量或算术表达式。数值大小的代数比较不考虑大小和用法子句。
对于非数字操作数
如果比较两个大小相等的非数字操作数，则将字符从左侧与相应位置进行比较，直到到达末尾。包含更多字符的操作数被声明为更大。
如果比较两个不等大小的非数字操作数，则在较短的数据项的末尾添加空格，直到操作数的大小相等为止，然后根据前面提到的规则进行比较。
下面给出的是Relation条件语句的语法-
[Data Name/Arithmetic Operation]
[IS] [NOT]
[Equal to (=),Greater than (>), Less than (=), Less than or equal (<=) ]
[Data Name/Arithmetic Operation]
例
IDENTIFICATION DIVISION.
PROGRAM-ID. HELLO.
DATA DIVISION.
WORKING-STORAGE SECTION.
01 WS-NUM1 PIC 9(9).
01 WS-NUM2 PIC 9(9).
PROCEDURE DIVISION.
A000-FIRST-PARA.
MOVE 25 TO WS-NUM1.
MOVE 15 TO WS-NUM2.
IF WS-NUM1 IS GREATER THAN OR EQUAL TO WS-NUM2 THEN
DISPLAY 'WS-NUM1 IS GREATER THAN WS-NUM2'
ELSE
DISPLAY 'WS-NUM1 IS LESS THAN WS-NUM2'
END-IF.
STOP RUN.
JCL执行上述COBOL程序-
//SAMPLE JOB(TESTJCL,XXXXXX),CLASS = A,MSGCLASS = C
//STEP1 EXEC PGM = HELLO
当您编译并执行上述程序时，它将产生以下结果-
WS-NUM1 IS GREATER THAN WS-NUM2
符号条件用于检查数字操作数的符号。它确定给定的数值是否大于，小于或等于零。
以下是Sign条件语句的语法-
[Data Name/Arithmetic Operation]
[IS] [NOT]
[Positive, Negative or Zero]
[Data Name/Arithmetic Operation]
例
IDENTIFICATION DIVISION.
PROGRAM-ID. HELLO.
DATA DIVISION.
WORKING-STORAGE SECTION.
01 WS-NUM1 PIC S9(9) VALUE -1234.
01 WS-NUM2 PIC S9(9) VALUE 123456.
PROCEDURE DIVISION.
A000-FIRST-PARA.
IF WS-NUM1 IS POSITIVE THEN
DISPLAY 'WS-NUM1 IS POSITIVE'.
IF WS-NUM1 IS NEGATIVE THEN
DISPLAY 'WS-NUM1 IS NEGATIVE'.
IF WS-NUM1 IS ZERO THEN
DISPLAY 'WS-NUM1 IS ZERO'.
IF WS-NUM2 IS POSITIVE THEN
DISPLAY 'WS-NUM2 IS POSITIVE'.
STOP RUN.
JCL执行上述COBOL程序-
//SAMPLE JOB(TESTJCL,XXXXXX),CLASS = A,MSGCLASS = C
//STEP1 EXEC PGM = HELLO
当您编译并执行上述程序时，它将产生以下结果-
WS-NUM1 IS NEGATIVE
WS-NUM2 IS POSITIVE
类条件用于检查操作数是否仅包含字母或数字数据。空格按字母顺序，字母下方和字母上方考虑。
以下是Class条件语句的语法-
[Data Name/Arithmetic Operation>]
[IS] [NOT]
[NUMERIC, ALPHABETIC, ALPHABETIC-LOWER, ALPHABETIC-UPPER]
[Data Name/Arithmetic Operation]
例
IDENTIFICATION DIVISION.
PROGRAM-ID. HELLO.
DATA DIVISION.
WORKING-STORAGE SECTION.
01 WS-NUM1 PIC X(9) VALUE 'ABCD '.
01 WS-NUM2 PIC 9(9) VALUE 123456789.
PROCEDURE DIVISION.
A000-FIRST-PARA.
IF WS-NUM1 IS ALPHABETIC THEN
DISPLAY 'WS-NUM1 IS ALPHABETIC'.
IF WS-NUM1 IS NUMERIC THEN
DISPLAY 'WS-NUM1 IS NUMERIC'.
IF WS-NUM2 IS NUMERIC THEN
DISPLAY 'WS-NUM2 IS NUMERIC'.
STOP RUN.
JCL执行上述COBOL程序-
//SAMPLE JOB(TESTJCL,XXXXXX),CLASS = A,MSGCLASS = C
//STEP1 EXEC PGM = HELLO
当您编译并执行上述程序时，它将产生以下结果-
WS-NUM1 IS ALPHABETIC
WS-NUM2 IS NUMERIC
条件名称是用户定义的名称。它包含一组由用户指定的值。它的行为类似于布尔变量。它们用级别编号88定义。它将没有PIC子句。
以下是用户定义条件语句的语法-
88 [Condition-Name] VALUE [IS, ARE] [LITERAL] [THRU LITERAL].
例
IDENTIFICATION DIVISION.
PROGRAM-ID. HELLO.
DATA DIVISION.
WORKING-STORAGE SECTION.
01 WS-NUM PIC 9(3).
88 PASS VALUES ARE 041 THRU 100.
88 FAIL VALUES ARE 000 THRU 40.
PROCEDURE DIVISION.
A000-FIRST-PARA.
MOVE 65 TO WS-NUM.
IF PASS
DISPLAY 'Passed with ' WS-NUM ' marks'.
IF FAIL
DISPLAY 'FAILED with ' WS-NUM 'marks'.
STOP RUN.
JCL执行上述COBOL程序-
//SAMPLE JOB(TESTJCL,XXXXXX),CLASS = A,MSGCLASS = C
//STEP1 EXEC PGM = HELLO
当您编译并执行上述程序时，它将产生以下结果-
Passed with 065 marks
否定条件是通过使用NOT关键字给出的。如果条件为真并且我们在其前面未给出NOT，则其最终值将为false。
以下是否定条件语句的语法-
IF NOT [CONDITION]
COBOL Statements
END-IF.
例
IDENTIFICATION DIVISION.
PROGRAM-ID. HELLO.
DATA DIVISION.
WORKING-STORAGE SECTION.
01 WS-NUM1 PIC 9(2) VALUE 20.
01 WS-NUM2 PIC 9(9) VALUE 25.
PROCEDURE DIVISION.
A000-FIRST-PARA.
IF NOT WS-NUM1 IS LESS THAN WS-NUM2 THEN
DISPLAY 'IF-BLOCK'
ELSE
DISPLAY 'ELSE-BLOCK'
END-IF.
STOP RUN.
JCL执行上述COBOL程序-
//SAMPLE JOB(TESTJCL,XXXXXX),CLASS = A,MSGCLASS = C
//STEP1 EXEC PGM = HELLO
当您编译并执行上述程序时，它将产生以下结果-
ELSE-BLOCK
组合条件包含两个或多个使用逻辑运算符AND或OR连接的条件。
以下是组合条件语句的语法-
IF [CONDITION] AND [CONDITION]
COBOL Statements
END-IF.
例
IDENTIFICATION DIVISION.
PROGRAM-ID. HELLO.
DATA DIVISION.
WORKING-STORAGE SECTION.
01 WS-NUM1 PIC 9(2) VALUE 20.
01 WS-NUM2 PIC 9(2) VALUE 25.
01 WS-NUM3 PIC 9(2) VALUE 20.
PROCEDURE DIVISION.
A000-FIRST-PARA.
IF WS-NUM1 IS LESS THAN WS-NUM2 AND WS-NUM1=WS-NUM3 THEN
DISPLAY 'Both condition OK'
ELSE
DISPLAY 'Error'
END-IF.
STOP RUN.
JCL执行上述COBOL程序-
//SAMPLE JOB(TESTJCL,XXXXXX),CLASS = A,MSGCLASS = C
//STEP1 EXEC PGM = HELLO
当您编译并执行上述程序时，它将产生以下结果-
Both condition OK
评估动词是一系列IF-ELSE语句的替代。它可以用于评估多个条件。它类似于C程序中的SWITCH语句。
例
IDENTIFICATION DIVISION.
PROGRAM-ID. HELLO.
DATA DIVISION.
WORKING-STORAGE SECTION.
01 WS-A PIC 9 VALUE 0.
PROCEDURE DIVISION.
MOVE 3 TO WS-A.
EVALUATE TRUE
WHEN WS-A > 2
DISPLAY 'WS-A GREATER THAN 2'
WHEN WS-A < 0
DISPLAY 'WS-A LESS THAN 0'
WHEN OTHER
DISPLAY 'INVALID VALUE OF WS-A'
END-EVALUATE.
STOP RUN.
JCL执行上述COBOL程序-
//SAMPLE JOB(TESTJCL,XXXXXX),CLASS = A,MSGCLASS = C
//STEP1 EXEC PGM = HELLO
当您编译并执行上述程序时，它将产生以下结果-
WS-A GREATER THAN 2