1. What is Pro*C?
Pro*C is an Oracle feature that allows embedding SQL statements directly in C/C++ programs. It is a precompiler, which converts the embedded SQL statements into standard C/C++ code.

2. Explain the steps involved in compiling a Pro*C program.
The steps involved in compiling a Pro*C program are:
– Precompilation: The Pro*C precompiler converts the program containing embedded SQL into pure C code.
– Compilation: The precompiler output is then compiled using a C/C++ compiler.
– Linking: The compiled Pro*C object file is linked with the Oracle libraries to generate the executable.

3. How can you connect to an Oracle database using Pro*C?
You can connect to an Oracle database using Pro*C by calling the `EXEC SQL CONNECT` statement with the necessary connection details such as username, password, and database name.

4. What is the difference between EXEC SQL and SQLCA in Pro*C?
– `EXEC SQL` is used to embed SQL statements directly in a Pro*C program.
– `SQLCA` is a host structure that holds information about the status of the most recently executed SQL statement. It is used to check for errors, retrieve row count, and handle database transaction errors.

5. How do you retrieve data from a cursor in Pro*C?
You can retrieve data from a cursor in Pro*C using the `EXEC SQL FETCH` statement. It fetches the next set of rows from the cursor and assigns the values to host variables.

6. Explain the use of the `EXEC SQL COMMIT` statement in Pro*C.
The `EXEC SQL COMMIT` statement commits the changes made in the database using SQL statements since the last commit or rollback statement. It makes the changes permanent.

7. What is a host variable in Pro*C?
A host variable is a C/C++ variable used to hold data from the database during runtime. Host variables are used to bind input data to SQL statements and retrieve output data from the database.

8. How do you pass values from host variables to SQL statements in Pro*C?
You can pass values from host variables to SQL statements in Pro*C by using the `:host_variable` notation. The value stored in the host variable is automatically bound to the corresponding placeholder in the SQL statement.

9. What is dynamic SQL in Pro*C?
Dynamic SQL refers to SQL statements that are constructed at runtime rather than being hardcoded in the program. In Pro*C, dynamic SQL can be achieved by using host variables and concatenating SQL strings.

10. Explain the use of the `EXEC SQL DECLARE` statement in Pro*C.
The `EXEC SQL DECLARE` statement is used to define a cursor in Pro*C. It associates a SQL query with a cursor name, allowing the program to fetch rows from the result set of the query.

11. How do you handle errors in Pro*C?
In Pro*C, errors can be handled using the `SQLCA.SQLCODE` variable. If the value of `SQLCA.SQLCODE` is positive or zero, it indicates successful execution. If it is negative, it indicates an error. Error handling code can be written using conditional statements based on `SQLCA.SQLCODE` values.

12. What is the purpose of the `INTO` clause in an SQL statement embedded in Pro*C?
The `INTO` clause in an SQL statement embedded in Pro*C is used to specify the host variables where the retrieved data from the database should be stored. It binds the selected values to the respective host variables.

13. What is the difference between a static cursor and a dynamic cursor in Pro*C?
– A static cursor is associated with a specific SQL query at compile time and the result set is fixed throughout the program’s execution.
– A dynamic cursor is defined at runtime and its SQL query can be changed during program execution.

14. Explain the use of the `EXEC SQL EXECUTE IMMEDIATE` statement in Pro*C.
The `EXEC SQL EXECUTE IMMEDIATE` statement is used for dynamic SQL execution in Pro*C. It allows the execution of a dynamically constructed SQL statement that is not known until runtime.

15. What is the purpose of using the `EXEC SQL INCLUDE` statement in Pro*C?
The `EXEC SQL INCLUDE` statement is used to include SQL precompiler-specific declarations and definitions in a Pro*C program. It provides access to Pro*C specific features and data types.

16. How do you handle NULL values in Pro*C?
NULL values can be handled in Pro*C by using nullable host variables. Before performing any operation or comparison, the program should check if the host variable is NULL using the `IS NULL` condition.

17. Explain the use of the `EXEC SQL ROLLBACK` statement in Pro*C.
The `EXEC SQL ROLLBACK` statement is used to undo all the changes made in the database since the last commit statement. It restores the state of the database to the last commit point.

18. What is a cursor in Pro*C?
A cursor in Pro*C is a database object used to retrieve and manipulate data from result sets. It allows navigation through the rows of a result set and provides methods to fetch, update, or delete rows.

19. What is the purpose of the `EXEC SQL INCLUDE SQLDA` statement in Pro*C?
The `EXEC SQL INCLUDE SQLDA` statement is used to include the SQL Descriptor Area (SQLDA) structure in a Pro*C program. SQLDA is used to retrieve information about the columns of a result set and bind host variables for data retrieval.

20. How do you prevent SQL injection attacks in Pro*C?
To prevent SQL injection attacks, it is recommended to use bind variables instead of concatenating user input directly into SQL statements. Bind variables ensure that the user input is treated as data and not as part of the SQL syntax, thus preventing malicious SQL injection.

1. What is Pro*C?
Pro*C is a pre-compiler that converts SQL statements embedded in C or C++ code into standard Oracle OCI (Oracle Call Interface) function calls.

2. How do you declare a host variable in Pro*C?
Host variables can be declared using the EXEC SQL statement. For example:
EXEC SQL BEGIN DECLARE SECTION;
int emp_id;
VARCHAR emp_name[30];
EXEC SQL END DECLARE SECTION;

3. What is the purpose of the EXEC SQL INCLUDE statement in Pro*C?
The EXEC SQL INCLUDE statement is used to include the necessary Pro*C header files for Oracle OCI function calls.

4. How do you retrieve multiple rows from a SELECT query in Pro*C?
You can use a cursor to retrieve multiple rows from a SELECT query. By using the FETCH statement in a loop, you can retrieve each row one by one.

5. What is a cursor in Pro*C?
A cursor is a database object that allows you to process individual rows returned by a SELECT statement. It provides a mechanism to retrieve and manipulate data from the result set.

6. How do you execute a dynamic SQL statement in Pro*C?
Dynamic SQL statements can be executed using the EXEC SQL statement. You need to concatenate the dynamic SQL string into a character variable and then execute it using the EXEC SQL EXECUTE IMMEDIATE statement.

7. How do you handle error conditions in Pro*C?
You can use the WHENEVER directive in Pro*C to specify what action should be taken when various error conditions occur. For example:
EXEC SQL WHENEVER SQLERROR GOTO handle_error;

8. How do you process a database exception in Pro*C?
You can use the SQLCA (SQL Communication Area) structure in Pro*C to retrieve information about the last database exception that occurred. The SQLCA variables provide information such as the error code and error message.

9. What is the purpose of the EXEC SQL COMMIT statement in Pro*C?
The EXEC SQL COMMIT statement is used to commit the current transaction and make all database changes permanent.

10. How do you pass values from host variables to SQL statements in Pro*C?
You can use the colon “:” character to bind a host variable to a placeholder in a SQL statement. For example:
EXEC SQL INSERT INTO employees (emp_id, emp_name)
VALUES (:emp_id, :emp_name);

11. What is the role of the Pro*C pre-compiler?
The Pro*C pre-compiler converts embedded SQL statements into standard C code. It handles the syntax validation of SQL statements and translates them into executable code.

12. How do you fetch only a specified number of rows using a cursor in Pro*C?
You can use the LIMIT clause in the SELECT statement to fetch a specified number of rows. For example:
EXEC SQL SELECT * FROM employees LIMIT 10;

13. What is the difference between Pro*C and Pro*COBOL?
Pro*C is a pre-compiler for embedding SQL in C or C++ code, while Pro*COBOL is a pre-compiler for embedding SQL in COBOL code.

14. How can you handle NULL values in host variables in Pro*C?
You can use the EXEC SQL IS NULL condition to check if a host variable holds a NULL value. For example:
EXEC SQL WHENEVER SQLERROR GOTO handle_error;
EXEC SQL SELECT emp_name INTO :emp_name FROM employees WHERE emp_id = :emp_id;
IF (emp_name IS NULL) THEN
// Handle NULL value
...
ENDIF;

15. How do you handle commit or rollback in Pro*C?
You can use the EXEC SQL COMMIT and EXEC SQL ROLLBACK statements to control the transaction in Pro*C. The COMMIT statement commits the current transaction, while the ROLLBACK statement rolls back the current transaction.

16. How do you handle date and time data types in Pro*C?
Date and time data types can be handled using the appropriate data type and format specifier in Pro*C. For example, you can use the VARCHAR data type to store date and time values in character format.

17. What is the purpose of the EXEC SQL INCLUDE SQLCA statement in Pro*C?
The EXEC SQL INCLUDE SQLCA statement is used to include the SQLCA structure definition in the Pro*C program. It allows access to the SQLCA variables for error handling and exception processing.

18. How do you fetch data from multiple tables using joins in Pro*C?
You can use the JOIN clause in the SELECT statement to fetch data from multiple tables based on the specified join condition. For example:
EXEC SQL SELECT e.emp_name, d.dept_name
FROM employees e
JOIN departments d
ON e.dept_id = d.dept_id;

19. How do you use arrays in Pro*C?
Arrays in Pro*C can be used to handle multiple rows from a result set or multiple values in a list. You can declare an array of host variables and use it with a cursor or loop to process multiple data.

20. How do you handle database exceptions in Pro*C?
You can handle database exceptions in Pro*C using exception handling code. The EXCEPTION block can be used to catch specific types of exceptions and perform appropriate error handling actions.