Variables and data types form the core building blocks of any C++ application, defining how data is stored, represented, and manipulated in memory. C++ is a statically typed language, meaning every variable must be declared with a specific data type (such as int, float, char, or bool) before use. Understanding fundamental types, modifiers (signed, unsigned, short, long), type casting mechanisms, and modern C++ type deduction (auto) is essential for writing efficient, type-safe, and high-performance software.
1. Which of the following is a fundamental data type in C++?
Correct Answer: c) int
Explanation:
In C++, 'int' is a built-in fundamental data type used to store integer values.
2. What is the guaranteed size of the 'char' data type in C++?
Correct Answer: a) 1 byte
Explanation:
The C++ standard guarantees that the size of a 'char' is exactly 1 byte.
3. Which keyword is used to represent boolean values in C++?
Correct Answer: b) bool
Explanation:
The 'bool' keyword is used in C++ to declare boolean variables holding true or false.
4. What does the 'void' data type indicate in C++?
Correct Answer: a) An empty set of values
Explanation:
The 'void' type specifies that no value is available, often used for functions returning nothing.
5. Which data type is used for storing double-precision floating-point numbers?
Correct Answer: b) double
Explanation:
The 'double' data type provides double-precision floating-point numbers, offering more precision than 'float'.
6. Which header file is required to use the std::string type?
Correct Answer: b)
Explanation:
The header must be included to use the C++ Standard Library std::string class.
7. What is the typical size of a 'float' variable on a 32-bit/64-bit architecture?
Correct Answer: b) 4 bytes
Explanation:
In most common architectures, a 'float' typically occupies 4 bytes (32 bits) in memory.
8. Which of the following generally determines the size of integer data types in C++?
Correct Answer: b) The compiler and system architecture
Explanation:
Aside from 'char', the exact sizes of types like 'int' depend on the compiler and hardware architecture.
9. What operator is used to find the size of a data type or variable in bytes?
Correct Answer: c) sizeof()
Explanation:
The 'sizeof' operator evaluates to the size, in bytes, of a specific variable or data type.
10. Which character type is commonly used to store wide characters in C++?
Correct Answer: b) wchar_t
Explanation:
'wchar_t' is the wide-character type used to represent characters requiring more memory, like Unicode.
11. Which type modifier can be applied to both 'int' and 'char'?
Correct Answer: c) unsigned
Explanation:
The 'unsigned' modifier can be applied to both integer and character types to restrict them to non-negative values.
12. What is the typical size of a 'short int'?
Correct Answer: b) 2 bytes
Explanation:
A 'short int' typically takes up 2 bytes of memory, storing values up to 32,767 (if signed).
13. What is the maximum value of an 8-bit unsigned char?
Correct Answer: c) 255
Explanation:
An 8-bit unsigned char holds values from 0 to (2^8 - 1), which equals 255.
14. What happens if you assign a negative value to an unsigned integer variable?
Correct Answer: d) The value wraps around to a large positive number
Explanation:
Assigning a negative value to an unsigned integer causes an underflow, wrapping around to a large positive value.
15. Which of the following is NOT a valid data type modifier in C++?
Correct Answer: d) medium
Explanation:
C++ supports 'short', 'long', 'signed', and 'unsigned'. 'medium' does not exist.
16. Which header file provides constants for the limits of integer types?
Correct Answer: b)
Explanation:
The header contains macros that define the minimum and maximum limits of integer types.
17. Which data type was standardized in C++11 to guarantee at least 64 bits?
Correct Answer: c) long long int
Explanation:
C++11 standardized 'long long int' to ensure a minimum width of 64 bits across platforms.
18. Can the 'unsigned' modifier be applied to standard floating-point types?
Correct Answer: b) No, it is a compilation error
Explanation:
The 'unsigned' modifier is strictly for integral types. Applying it to 'float' or 'double' causes a compilation error.
19. Is the plain 'char' type signed or unsigned by default?
Correct Answer: c) Implementation-defined
Explanation:
The C++ standard leaves whether plain 'char' is signed or unsigned up to the compiler implementation.
20. Which combination of modifiers is syntactically invalid?
Correct Answer: c) long short int
Explanation:
You cannot combine 'long' and 'short' together on the same variable, as they are conflicting size requirements.
21. Which of the following is a valid variable name in C++?
Correct Answer: b) *myVar
Explanation:
Variables can start with an underscore or letter. They cannot start with a number, contain spaces, or use hyphens.
22. Are variable names in C++ case-sensitive?
Correct Answer: a) Yes
Explanation:
C++ is highly case-sensitive. Variables named 'count' and 'Count' are treated as completely distinct identifiers.
23. Which of the following cannot be used as a variable name?
Correct Answer: c) class
Explanation:
'class' is a reserved keyword in C++ and cannot be used as a programmer-defined identifier.
24. What happens if a variable name starts with two consecutive underscores?
Correct Answer: b) It is reserved for compiler implementations
Explanation:
Identifiers containing double underscores are reserved for the C++ standard library and compiler usage.
25. What is the maximum strict limit for the length of a variable name in the C++ standard?
Correct Answer: d) No strict standard limit
Explanation:
The C++ standard defines no strict maximum length for identifiers, though individual compilers might impose practical limits.
26. Which symbol is allowed within a C++ variable name?
Correct Answer: c) *
Explanation:
Only letters, digits, and underscores (*) are permitted in standard C++ variable names.
27. Is 'int return = 5;' a valid C++ statement?
Correct Answer: b) No, because 'return' is a keyword
Explanation:
Keywords are reserved words in C++ and cannot be used as variable names.
28. Which of these is considered standard naming convention for local variables in modern C++?
Correct Answer: a) camelCase or snake_case
Explanation:
camelCase and snake_case are standard for variables, while PascalCase is used for classes, and UPPER_CASE for macros.
29. Why is 'int num-ber = 10;' invalid?
Correct Answer: a) Hyphens are parsed as the subtraction operator
Explanation:
Hyphens are interpreted by the compiler as the minus (subtraction) operator, making them invalid inside identifier names.
30. Can a variable name consist of only a single underscore '* '?
Correct Answer: c) Yes, it is a valid identifier
Explanation:
A single underscore is syntactically a valid identifier, though generally avoided for clarity.
31. What is the value of an uninitialized local integer variable?
Correct Answer: b) Garbage value
Explanation:
Uninitialized local variables contain whatever raw data was previously left at their memory location, known as a garbage value.
32. What is the default value of an uninitialized global integer variable?
Correct Answer: a) 0
Explanation:
Global and static variables are zero-initialized by default before main() runs.
33. What does the statement 'extern int a;' do?
Correct Answer: c) Declares variable 'a' without defining it
Explanation:
The 'extern' keyword tells the compiler that the variable 'a' exists and its memory allocation is in another translation unit.
34. Which of the following demonstrates C++11 uniform (list) initialization?
Correct Answer: c) int x{5};
Explanation:
Using curly braces {} for initialization is known as list initialization or uniform initialization, introduced in C++11.
35. What is a major safety advantage of brace initialization 'int x{5.5};'?
Correct Answer: b) It prevents narrowing conversions by throwing an error
Explanation:
Brace initialization forbids narrowing conversions; trying to initialize an int with a float via braces causes a compilation error.
36. Which of the following is a valid multiple declaration?
Correct Answer: a) int a, b = 10;
Explanation:
Multiple variables of the same type can be declared on a single line by separating them with commas.
37. What is an L-value in C++?
Correct Answer: b) An expression that refers to an identifiable memory location
Explanation:
An L-value represents an object that occupies an identifiable location in memory, allowing it to appear on the left side of an assignment.
38. What is an R-value in C++?
Correct Answer: c) A temporary value that does not persist beyond the expression
Explanation:
An R-value is typically a temporary literal or expression result that does not have a persistent memory address.
39. In the statement 'int x = y;', 'y' must be declared before this line. True or False?
Correct Answer: a) True
Explanation:
C++ strictly requires all identifiers (variables) to be declared before they are used in any expression.
40. Which initialization syntax is explicitly known as direct initialization?
Correct Answer: b) int x(5);
Explanation:
Direct initialization uses parentheses to initialize a variable, invoking its constructor directly.
41. What is the scope of a standard local variable?
Correct Answer: c) The block or function it is declared in
Explanation:
Local variables are only accessible within the specific code block {} or function where they are defined.
42. Which operator allows accessing a global variable when a local variable has the exact same name?
Correct Answer: c) ::
Explanation:
The scope resolution operator (::) tells the compiler to access the global scope version of the variable.
43. What is the lifetime of a variable declared with the 'static' keyword inside a function?
Correct Answer: b) It persists for the duration of the entire program
Explanation:
A local static variable is initialized once and retains its value between function calls until the program terminates.
44. What happens when an inner block declares a variable with the same name as a variable in an outer block?
Correct Answer: c) The inner variable shadows (hides) the outer variable
Explanation:
Variable shadowing occurs when a variable in an inner scope has the same name as one in an outer scope, temporarily hiding it.
45. What defines a global variable?
Correct Answer: b) A variable defined outside of all functions
Explanation:
Global variables are defined outside any function or block, making them globally accessible to the program.
46. What is the scope of a 'static' global variable?
Correct Answer: b) Only the file it is declared in
Explanation:
When 'static' is applied to a global variable, it gives it internal linkage, making it visible only within its own translation unit.
47. Variables dynamically allocated using the 'new' keyword are stored where?
Correct Answer: c) The Heap
Explanation:
Dynamic memory allocation using 'new' creates variables on the heap (free store).
48. Automatic variables created normally inside a function are stored where?
Correct Answer: a) The Stack
Explanation:
Automatic local variables are pushed onto the call stack and popped when they go out of scope.
49. What did the 'register' keyword originally suggest to the compiler?
Correct Answer: b) Store the variable in CPU registers for fast access
Explanation:
Historically, 'register' requested the compiler to store the variable in a CPU register for speed (deprecated in modern C++).
50. Which keyword specifies that each thread has its own separate instance of a variable?
Correct Answer: c) thread_local
Explanation:
The 'thread_local' keyword specifies thread storage duration, creating a unique instance of the variable per thread.
51. What does the 'const' keyword do to a variable?
Correct Answer: b) Prevents it from being modified after initialization
Explanation:
'const' creates a constant value, causing a compile error if code attempts to modify it.
52. When must a 'const' variable be initialized?
Correct Answer: b) Exactly at the time of its declaration
Explanation:
Because a const variable cannot be assigned a value later, it must be initialized exactly when declared.
53. What is the primary difference between 'const' and 'constexpr'?
Correct Answer: b) constexpr is evaluated at compile-time; const can be runtime
Explanation:
'constexpr' guarantees that the variable is evaluated at compile time, while 'const' just guarantees immutability, even if initialized at runtime.
54. What does 'const int* ptr' mean?
Correct Answer: b) The integer being pointed to cannot be modified through this pointer
Explanation:
This is a pointer to a constant integer. The memory address can change, but the value it points to cannot be altered via the pointer.
55. What does 'int* const ptr' mean?
Correct Answer: a) The pointer itself cannot change, but the value it points to can
Explanation:
This is a constant pointer. The address it holds is locked, but the actual integer data can be modified.
56. Which of the following is NOT an advantage of 'const' over '#define'?
Correct Answer: d) #define cannot handle strings
Explanation:
#define can handle string literals easily. The other statements are true advantages of using const.
57. What does the 'volatile' keyword signify?
Correct Answer: b) The variable's value may change externally, so the compiler shouldn't optimize it
Explanation:
'volatile' warns the compiler that a variable might be modified by hardware or other threads, preventing aggressive caching optimizations.
58. Which keyword allows a class member to be modified even if the class instance is 'const'?
Correct Answer: b) mutable
Explanation:
The 'mutable' keyword overrides 'const', allowing specific members to be modified inside a constant object.
59. By default, what linkage does a global 'const' variable have in C++?
Correct Answer: b) Internal linkage
Explanation:
In C++, global const variables have internal linkage by default, meaning they are restricted to their own translation unit unless declared extern.
60. Which specific C++ cast is used to cast away the 'const' qualifier?
Correct Answer: a) const_cast
Explanation:
'const_cast' is uniquely designed to strip or add 'const' and 'volatile' qualifiers from pointers or references.
61. What happens when you assign a 'float' value to an 'int' variable?
Correct Answer: b) The fractional part is simply truncated
Explanation:
Implicit conversion from float/double to int strictly truncates (drops) the decimal portion without rounding.
62. Which casting operator is used for standard, compile-time type conversions?
Correct Answer: d) static_cast
Explanation:
'static_cast' performs standard conversions (like float to int) and checks safety at compile time.
63. Which cast is designed specifically for safe downcasting in class hierarchies with virtual functions?
Correct Answer: a) dynamic_cast
Explanation:
'dynamic_cast' performs runtime type checking to safely cast pointers/references within polymorphic class hierarchies.
64. What happens if a 'dynamic_cast' fails on a pointer?
Correct Answer: b) It returns nullptr
Explanation:
If a dynamic_cast fails when casting pointers, it safely returns nullptr. (If it fails on a reference, it throws std::bad_cast).
65. Which cast is the most dangerous, converting between unrelated pointers or integer types?
Correct Answer: c) reinterpret_cast
Explanation:
'reinterpret_cast' overrides the type system, interpreting the raw memory as a completely different type.
66. What is integer promotion in C++?
Correct Answer: b) Automatically converting smaller integer types to 'int' for arithmetic
Explanation:
Types smaller than int (like char or short) are implicitly promoted to int before performing arithmetic operations.
67. When casting an integer to a boolean, what does the number 0 become?
Correct Answer: b) false
Explanation:
In C++, the integer 0 implicitly converts to the boolean value 'false'.
68. When casting an integer to a boolean, what does the number -5 become?
Correct Answer: a) true
Explanation:
Any non-zero integer (positive or negative) implicitly converts to 'true'.
69. What is '(int)x' an example of?
Correct Answer: b) Explicit C-style casting
Explanation:
Using parentheses with a type name before a variable is the syntax for an explicit C-style cast.
70. What does the 'typeid' operator do?
Correct Answer: a) Returns a std::type_info object containing type information at runtime
Explanation:
'typeid' is part of RTTI (Run-Time Type Information) and returns type details of an expression.
71. What does the 'auto' keyword do in modern C++?
Correct Answer: b) Deduces the type of a variable from its initializer at compile time
Explanation:
'auto' tells the compiler to deduce the variable's type based on the right-hand side expression.
72. Can you declare a variable with 'auto' without initializing it (e.g., auto x;)?
Correct Answer: b) No
Explanation:
Because 'auto' deduces the type from the initialization value, the variable must be initialized immediately.
73. If 'int x = 5;', what type does 'auto y = &x;' deduce?
Correct Answer: c) int*
Explanation:
The '&' operator takes the address, returning a pointer. Thus, 'auto' deduces 'int*'.
74. Which keyword inspects the exact type of an expression without evaluating it?
Correct Answer: d) decltype
Explanation:
'decltype' determines the exact type of an expression at compile time without executing the expression itself.
75. What is 'nullptr' introduced in C++11?
Correct Answer: c) A keyword representing a type-safe null pointer literal
Explanation:
'nullptr' provides a type-safe pointer constant (of type std::nullptr_t), unlike NULL which is just an integer 0.
76. Which data type was introduced specifically for UTF-16 character encoding?
Correct Answer: a) char16_t
Explanation:
C++11 added 'char16_t' to explicitly support UTF-16 Unicode character representation.
77. Does 'auto' retain top-level 'const' qualifiers by default?
Correct Answer: b) No
Explanation:
When copying a value, 'auto' strips top-level const qualifiers. You must write 'const auto' to keep it constant.
78. What feature allows unpacking tuples or structs into multiple variables easily (C++17)?
Correct Answer: b) Structured bindings
Explanation:
Structured bindings (e.g., auto [x, y] = myPair;) unpack structures or tuples into individual variable names.
79. What is 'std::byte' (introduced in C++17)?
Correct Answer: c) A distinct type implementing raw memory without arithmetic operations
Explanation:
std::byte provides a type-safe representation of memory bytes, supporting bitwise operations but intentionally lacking math operations.
80. Unlike 'auto', does 'decltype' retain 'const' and reference qualifiers?
Correct Answer: a) Yes
Explanation:
Unlike auto, decltype precisely deduces the exact type, retaining all const and reference qualifiers.
81. What is the primary purpose of the 'typedef' keyword?
Correct Answer: b) To create an alias for an existing data type
Explanation:
'typedef' allows programmers to create custom name aliases for existing, often complex, types.
82. Which C++11 keyword provides a modern, template-compatible alternative to 'typedef'?
Correct Answer: c) using
Explanation:
The 'using' keyword (e.g., using Integer = int;) acts as a modern alternative to typedef and supports templates.
83. What is an 'enum' in C++?
Correct Answer: c) A user-defined type consisting of a set of named integer constants
Explanation:
An enumeration defines a custom type restricted to a specific set of named integer values.
84. Unless explicitly assigned, what integer value does the first item in a standard enum take?
Correct Answer: a) 0
Explanation:
By default, enumerators begin at 0 and increment by 1.
85. What is the main safety advantage of an 'enum class' over a traditional 'enum'?
Correct Answer: c) It prevents implicit conversion to integers and scopes the names
Explanation:
Enum classes provide strong type safety by not implicitly casting to int and by requiring scoped access (e.g., Color::Red).
86. Can you specify the underlying data type of an enum class (e.g., to save memory)?
Correct Answer: b) Yes, by adding a colon and the type (e.g., enum class Color : char)
Explanation:
C++11 allows explicit specification of the underlying integer type for an enum to optimize memory usage.
87. What is the fundamental difference between a 'struct' and a 'class' in C++?
Correct Answer: b) Struct members are public by default; class members are private by default
Explanation:
In C++, the only functional difference between a struct and a class is default visibility.
88. What is a 'union' data type?
Correct Answer: c) A type where all members share the exact same memory location
Explanation:
A union holds different data types but stores them in the exact same memory space, meaning only one member is valid at a time.
89. What dictates the memory size of a 'union'?
Correct Answer: b) The size of its largest member
Explanation:
To ensure it can hold any of its members safely, a union's size is determined by its largest data member.
90. What are bit-fields in C++ structs?
Correct Answer: b) Variables specifying their exact memory size in bits
Explanation:
Bit-fields allow you to tightly pack data by specifying the exact number of bits an integer member will consume.
91. What is the size of an entirely empty struct or class in C++?
Correct Answer: b) 1 byte
Explanation:
C++ requires every distinct object to have a unique memory address, so an empty class/struct is assigned a size of at least 1 byte.
92. What is the size of a standard pointer variable on a 64-bit system?
Correct Answer: c) 8 bytes
Explanation:
Memory addresses on a 64-bit system are 64 bits wide, which equates to 8 bytes of memory.
93. What does a 'void*' (void pointer) represent?
Correct Answer: b) A generic pointer that can hold the address of any data type
Explanation:
A void pointer is a generic pointer type that can store the address of any object without knowing its type.
94. Can you directly dereference a 'void*' pointer?
Correct Answer: b) No, it must be explicitly cast to a specific type first
Explanation:
Because the compiler doesn't know the size or type of the underlying data, a void pointer cannot be dereferenced directly.
95. What is a reference variable ('&') in C++?
Correct Answer: b) An alternative name (alias) for an already existing variable
Explanation:
A reference acts as an alias. Changes made through the reference directly modify the original aliased variable.
96. Can a reference variable be left uninitialized upon declaration?
Correct Answer: b) No
Explanation:
A reference must always be initialized to alias an existing variable exactly at the time of its declaration.
97. Can a reference be changed to alias a completely different variable later in the program?
Correct Answer: b) No, it is bound permanently upon initialization
Explanation:
Once a reference is bound to an object, it cannot be reseated. Any assignment modifies the bound object, not the reference itself.
98. What happens when a raw array is passed into a C++ function?
Correct Answer: c) It decays into a pointer to its first element
Explanation:
Raw arrays 'decay' into a pointer to their first element, which is why size information is lost when passing to functions.
99. What is the primary difference between a C-string and a C++ std::string?
Correct Answer: b) std::string manages its own memory and length, while a C-string is just a null-terminated char array
Explanation:
C-strings require manual memory and terminator management, whereas std::string is an object managing its own dynamic memory.
100. Can you declare an array of references in C++ (e.g., int& arr[5];)?
Correct Answer: b) No, it is explicitly illegal in C++
Explanation:
C++ forbids arrays of references because references are not distinct objects and do not take up standalone memory in an array context.
