面试题与答案

COBOL (Common Business-Oriented Language) is a high-level programming language used primarily for business, finance, and administrative systems.

The PERFORM statement is used for loop control in COBOL. It allows the repeated execution of a set of statements until a specified condition is met.

Example:

PERFORM 5 TIMES
  DISPLAY 'Hello, World!'
END-PERFORM.

The INITIALIZE verb is used to set the initial values for data items in COBOL. It initializes numeric items to zero and alphanumeric items to spaces.

Example:

01 COUNT PIC 9(3).
INITIALIZE COUNT.

The FILE SECTION in COBOL is used to describe the structure and attributes of files used by the program. It includes the FD (File Description) entries.

COBOL provides the COMPUTE statement for decimal arithmetic. It allows the programmer to perform arithmetic operations on numeric data items with explicit precision.

Example:

COMPUTE TOTAL = AMOUNT-1 + AMOUNT-2.

The LEVEL number in COBOL is used to indicate the hierarchy and nesting level of data items. It determines the structure and organization of data in the Data Division.

Example:

01 EMPLOYEE-RECORD.
  05 EMPLOYEE-ID PIC 9(5).
  05 EMPLOYEE-NAME PIC X(20).

Data movement in COBOL is achieved through the MOVE verb. It transfers the value of one data item to another, and it can handle various data types.

Example:

MOVE 100 TO AMOUNT.

COBOL supports file processing through file control entries in the File Section. The OPEN, READ, WRITE, and CLOSE statements are used for file operations.

Example:

OPEN INPUT FILE-1.
READ FILE-1 INTO DATA-RECORD.
CLOSE FILE-1.

The SET statement in COBOL is used to assign values to index names, condition names, and other special registers. It is essential for controlling program flow.

Example:

SET EMPLOYEE-INDEX TO 1.

The INITIALIZE verb in COBOL is used to set the initial values for data items. It initializes numeric items to zero and alphanumeric items to spaces.

Example:

01 COUNT PIC 9(3).
INITIALIZE COUNT.

The COPY statement in COBOL is used for including copybooks in the source code. It allows the reuse of common code and improves maintainability.

Example:

COPY 'COMMON-FILE'.

The ACCEPT statement in COBOL is used for interactive input. It allows the program to receive data directly from the user during runtime.

Example:

ACCEPT EMPLOYEE-NAME.

The WORKING-STORAGE section in COBOL is used to declare variables that retain their values throughout the execution of the program. It provides working storage for temporary data.

Example:

WORKING-STORAGE SECTION.
01 COUNTER PIC 9(3) VALUE 0.

The CALL statement in COBOL is used to invoke subprograms or procedures from other programs. It allows modular programming and code reuse.

Example:

CALL 'SUB-PROGRAM' USING PARAMETER-1 PARAMETER-2.

The END-IF statement in COBOL marks the end of an IF statement block. It is used to indicate the conclusion of the conditional code and resume normal program flow.

Example:

IF AMOUNT > LIMIT
  DISPLAY 'Amount exceeds limit'
END-IF.

The ACCEPT FROM statement in COBOL is used to receive data directly from an external device, such as a keyboard. It simplifies interactive input operations.

Example:

ACCEPT WS-EMPLOYEE-ID FROM 'Enter Employee ID:'.

The COMPUTATIONAL-3 (COMP-3) clause in COBOL is used to define packed-decimal data items. It represents decimal numbers in a packed format for efficient storage.

Example:

01 AMOUNT PIC 9(5) COMP-3.

The Division structure in COBOL consists of Identification, Environment, Data, and Procedure divisions. These divisions help organize the program's structure.

COMP and COMP-3 are data types in COBOL. COMP is used for binary representation, while COMP-3 is used for packed decimal representation.

CALL is used to transfer control to another program or a specific paragraph within the same program. PERFORM is used for looping and invoking paragraphs or sections.

Indexing in COBOL is typically done using INDEXED BY clause. It associates an index name with a data item, allowing for efficient access to table elements.

Example:

01 EMPLOYEE-TABLE OCCURS 10 TIMES INDEXED BY EMPLOYEE-INDEX.
...

Static calls are resolved at compile-time, while dynamic calls are resolved at run-time. CALL and PERFORM are examples of static calls, while CALL 'subprogram' USING ... is a dynamic call.

The 88 level in COBOL is used for condition names. It allows the programmer to associate a condition with a data item, simplifying the writing of conditionals.

Example:

01 STATUS-CODE PIC 99.
88 SUCCESS VALUE 00.
88 FAILURE VALUE 01.

The OCCURS clause in COBOL is used to define arrays or tables. It specifies the number of occurrences or elements, allowing for efficient handling of repetitive data.

Example:

01 SALES-AMOUNT OCCURS 12 TIMES PIC 9(5).

The INSPECT verb in COBOL is used for string manipulation. It allows the programmer to search, replace, or delete characters in a string.

Example:

INSPECT NAME-STRING REPLACING ALL '- ' BY SPACE.

The EVALUATE statement in COBOL is used for multi-way branching. It simplifies complex nested IF statements and enhances code readability.

Example:

EVALUATE TRUE
  WHEN AGE < 18 DISPLAY 'Minor'
  WHEN AGE > 65 DISPLAY 'Senior'
  WHEN OTHER DISPLAY 'Adult'.

The INDEXED BY clause in COBOL is used to associate an index name with a table or array. It provides a way to reference individual elements efficiently.

Example:

01 EMPLOYEE-TABLE OCCURS 10 TIMES INDEXED BY EMPLOYEE-INDEX.
...

The PERFORM VARYING statement in COBOL is used for iterative processing. It allows a specified set of statements to be repeated while incrementing or decrementing a loop variable.

Example:

PERFORM VARYING I FROM 1 BY 1 UNTIL I > 10
  DISPLAY 'Iteration ' I.
END-PERFORM.

COBOL provides the special registers CURRENT-DATE and CURRENT-TIME to handle date and time operations. These registers store system date and time values.

Example:

MOVE FUNCTION CURRENT-DATE TO DATE-FIELD.

COBOL supports data validation through the use of conditions, the IF statement, and the EVALUATE statement. These constructs help ensure data integrity.

Example:

IF AMOUNT < 0
  DISPLAY 'Invalid amount'
END-IF.

The EXIT statement in COBOL is used to terminate a loop prematurely. It allows the program to exit a PERFORM loop or a Section before reaching the normal end.

Example:

PERFORM UNTIL EOF-FLAG = 'Y'
  ...
  IF SOME-CONDITION
    EXIT.
  END-IF.
END-PERFORM.

The USAGE clause in COBOL is used to specify the internal representation of data items. It defines how data is stored in memory, such as binary, packed-decimal, or display.

Example:

01 AMOUNT PIC 9(5) USAGE COMP-3.

The MOVE CORRESPONDING statement in COBOL is used to move corresponding data items from one record to another. It simplifies the process of copying similar fields between records.

Example:

MOVE CORRESPONDING RECORD-1 TO RECORD-2.

The SEARCH statement in COBOL is used to search a table for a specified value. It is commonly used with the WHEN clause to perform conditional actions based on the search result.

Example:

SEARCH ITEM-TABLE AT END DISPLAY 'Item not found'.

The STRING statement in COBOL is used for string concatenation. It allows the programmer to concatenate and manipulate character strings efficiently.

Example:

STRING 'Hello' ' ' 'World' DELIMITED BY SIZE INTO OUTPUT-STRING.

The UNSTRING statement in COBOL is used to break down a delimited string into its individual components. It is useful for parsing and extracting data from strings.

Example:

UNSTRING NAME-STRING DELIMITED BY ',' INTO FIRST-NAME LAST-NAME.

The INDEX in COBOL is a special register that is used to store the position within a table. It is often manipulated using the SET and PERFORM statements.

Example:

SET TABLE-INDEX TO 1.

The EXIT PARAGRAPH statement in COBOL is used to exit a specific paragraph prematurely. It is useful for controlling the flow within a section of code.

Example:

PERFORM PROCESS-DATA.
IF ERROR-FLAG = 'Y' THEN
  EXIT PARAGRAPH.
END-IF.

The USE statement in COBOL is used to declare and specify the usage of indexes in a SEARCH statement. It associates an index with a table to optimize search operations.

Example:

USE EMPLOYEE-INDEX.

The EXIT SECTION statement in COBOL is used to terminate the current section prematurely. It allows the program to skip the remaining code within a particular section.

Example:

PERFORM PROCESS-DATA SECTION.
IF ERROR-FLAG = 'Y' THEN
  EXIT SECTION.
END-IF.

Errors in COBOL programs are often handled using the ON EXCEPTION clause or the use of condition names. This allows for the graceful handling of errors.

Example:

READ FILE-1 INTO WS-RECORD ON EXCEPTION
  DISPLAY 'Error reading file'
END-READ.

The REDEFINES clause in COBOL is used to share storage between two or more data items. It allows multiple data descriptions for the same physical storage.

Example:

01 EMPLOYEE-NAME PIC X(20).
01 EMPLOYEE-NAME-REDEFINED REDEFINES EMPLOYEE-NAME PIC 9(9).

The MERGE statement in COBOL is used to merge two or more sorted input files into a single sorted output file. It is often used for sorting and merging files.

Example:

MERGE FILE-1, FILE-2 INTO SORTED-FILE.

The REWRITE statement in COBOL is used to modify the contents of a record in a file. It is typically used in conjunction with the READ statement to update existing records.

Example:

READ FILE-1 INTO DATA-RECORD.
REWRITE DATA-RECORD.

The EXIT PROGRAM statement in COBOL is used to terminate the entire program. It is often used in conjunction with a condition or as part of an error-handling routine.

Example:

IF ERROR-FLAG = 'Y' THEN
  EXIT PROGRAM.
END-IF.

The RESERVE statement in COBOL is used to allocate storage space for large data items. It ensures that sufficient memory is reserved to accommodate the specified data.

Example:

01 LARGE-DATA PIC X(1000).
RESERVE 1000 CHARACTERS FOR LARGE-DATA.

The SET ENVIRONMENT statement in COBOL is used to specify or change environment settings, such as the currency symbol, decimal point character, or date format.

Example:

SET ENVIRONMENT CURRENCY-SYMBOL '$'.

The REJECT statement in COBOL is used to return a record to an input file after it has been read. It is often used in conjunction with the REWRITE statement.

Example:

READ INPUT-FILE INTO DATA-RECORD.
IF CONDITION
  REJECT DATA-RECORD.
END-IF.

The ALTER statement in COBOL is used to modify the properties of data items at runtime. It allows dynamic changes to the length, picture, or usage of data items.

Example:

ALTER ITEM-DESCR TO PIC X(30).

The GENERATE statement in COBOL is used to dynamically create new paragraphs or sections during program execution. It enhances the flexibility and adaptability of the program.

Example:

GENERATE 'NEW-PARAGRAPH'.