Programming Languages Quiz: RPG, SQL, C#, and C++

Encapsulation is a fundamental object-oriented programming concept that binds together data and the functions that manipulate them into a single unit called a class.

Statement (a) is false - struct members are public by default in C++ (class members are private by default). Statement (b) is true - new and delete operators can be overloaded. Statement (c) is technically incorrect because the subscript operator [] and assignment operator = must be non-static member functions, not friend functions.

In C++, if no return type is specified for a function, the default return type is 'int'. This is a legacy feature from C. However, it's considered poor practice - always explicitly specify the return type. The 'void' return type means the function returns nothing, while 'bool' is for boolean return values.

In C#, boxing converts value types to reference types, and unboxing reverses this. During boxing, the runtime creates a temporary reference type object on the heap to hold the value type. Reference types are stored on the heap, not the stack (option A is wrong), and identifiers can contain numeric characters (option D is wrong).

C# allows multiple Main() methods in different classes, but you must specify which one is the entry point using compiler options. The compiler returns an error if multiple Main() methods exist without an explicit entry point specification. Option A is wrong because you CAN define multiple Main() methods.

C# identifiers are names for variables, classes, structs, etc. They must begin with a letter or underscore, are case-sensitive (option B is wrong), and can contain numeric characters after the first character (option D is wrong).

In C#, you cannot use keywords as identifiers unless they are prefixed with '@'. Identifiers can also contain Unicode characters, making both statements correct.

Both structs and classes serve as templates for object creation (option A), and both use the 'new' keyword to instantiate (option C). However, option B is incorrect because structs are value types stored on the stack (or inline), while classes are reference types stored on the heap.

Boxing converts value types to reference types by creating an object on the heap and copying the value type value there (Option B and D are correct). Option A is wrong because value types are stored on stack, not heap. Option C is incorrect because unboxing converts reference types back to value types, not value to reference.

In Oracle SQL, table/column names cannot be reserved words (like SELECT, FROM, etc.) without quoting. Column aliases (defined in SELECT clause) cannot be used in WHERE clause because WHERE is processed before SELECT. Names are case-insensitive and must start with a letter.

In relational database theory, a table is called a relation. In ER (Entity-Relationship) modeling, a table representing an entity type can be called an entity. Records and fields refer to data within the table (rows and columns), not the table structure itself.

Normalization is the formal process of structuring data into relational tables to eliminate redundancy and improve data integrity. It involves organizing columns and tables to minimize data duplication and dependency, which is the foundation of relational database design.

DML (Data Manipulation Language) commands operate on existing data within database objects. SELECT retrieves data, INSERT adds new rows, UPDATE modifies existing data, and DELETE removes rows. CREATE and ALTER are DDL (Data Definition Language) commands that define or modify database structures, not manipulate data.

Indexes are beneficial when columns contain wide range of values (high cardinality), when tables are large (performance impact is significant), and when columns contain many NULL values (indexes can efficiently skip NULLs). Columns that are infrequently used don't benefit from indexing as the query performance gain wouldn't justify the storage and maintenance overhead.

EXCPT (Exception Output) in RPG is specifically designed to update only selected fields on a record when certain conditions are met, rather than writing entire records. EXFMT writes formatted display records, UPDAT is not a valid RPG operation code, and WRITE creates new records rather than updating existing ones.

In RPG/400, the maximum number of files that can be declared and specified in a single program is limited to 50.

The RPG code sets STRING='ABCDEF', then uses SUBST to extract a 2-character substring starting at position 2 (C is the second character in 'ABCDEF'). The substring operation extracts positions 2-3, which gives 'CD'. MOVEL copies 'ABCDEF' left-justified into STRING, and SUBST with factor 2=2 and length=90 (effectively 2) extracts from position 2.

In IBM i (AS/400) environments, message CPF4131 is a standard diagnostic message that indicates a level check error between a file definition and the program accessing it.

DSPOBJLCK (Display Object Locks) is the correct IBM i command to show active locks on any object. DSPLCK is not a valid command, DSPSYSLCK would display system-level locks (not object-specific), and DSPACTLCK is not a standard command.