5.3.1 - Overview of Unions and Structure vs Union.

1. What is a union in C?

(A) A user-defined data type that stores different types of data in the same memory location
(B) A pre-defined data type
(C) A type used to create arrays
(D) A structure within a class

Correct Answer: (A) A user-defined data type that stores different types of data in the same memory location

2. How much memory does a union occupy?

(A) Equal to the sum of all its members
(B) Equal to the size of the largest member
(C) Equal to half the size of all its members
(D) Equal to the size of the first member

Correct Answer: (B) Equal to the size of the largest member

3. Which keyword is used to declare a union in C?

(A) struct
(B) union
(C) enum
(D) typedef

Correct Answer: (B) union

4. How are union members accessed in C?

(A) Using the arrow (->) operator
(B) Using the colon (:) operator
(C) Using the dot (.) operator
(D) Using the star (*) operator

Correct Answer: (C) Using the dot (.) operator

5. Which of the following is a correct way to declare a union?

(A) union { int a; float b; };
(B) union example { int a; float b; };
(C) union example(int a, float b);
(D) example union { int a; float b; };

Correct Answer: (B) union example { int a; float b; };

6. What happens when you assign a value to a member of a union?

(A) All members of the union get updated
(B) Only the last assigned member holds a valid value
(C) All members of the union are allocated memory
(D) All values in the union are saved

Correct Answer: (B) Only the last assigned member holds a valid value

7. How does the memory allocation for a union differ from that of a structure?

(A) Union uses more memory than a structure
(B) Structure uses less memory than a union
(C) Union allocates memory for only one member at a time
(D) Structure and union both allocate the same memory

Correct Answer: (C) Union allocates memory for only one member at a time

8. Which is true regarding unions in C?

(A) Multiple members of a union can store values simultaneously
(B) Only one member of a union can store a value at a time
(C) Union members have individual memory locations
(D) All members of a union can be accessed at once

Correct Answer: (B) Only one member of a union can store a value at a time

9. What is the size of the union below if char is 1 byte, int is 4 bytes, and float is 4 bytes?

                union example {
                    char ch;
                    int a;
                    float b;
                };

(A) 1 byte
(B) 4 bytes
(C) 9 bytes
(D) 4 bytes

Correct Answer: (D) 4 bytes

10. What is the primary advantage of using a union over a structure?

(A) Reduced memory usage
(B) Faster access to members
(C) Ability to store more data
(D) Improved program readability

Correct Answer: (A) Reduced memory usage

11. How can you declare a variable for a union named data in C?

(A) union data d;
(B) union d data;
(C) data union d;
(D) d union data;

Correct Answer: (A) union data d;

12. What will be the output of the following code if char is 1 byte and int is 4 bytes?

                union example {
                    char ch;
                    int a;
                };
                union example ex;
                printf("%lu", sizeof(ex));

(A) 1
(B) 4
(C) 5
(D) 8

Correct Answer: (B) 4

13. Which of the following is a valid difference between unions and structures?

(A) Union members share the same memory, while structure members do not
(B) Structures are faster than unions
(C) Union can store more data than a structure
(D) Structures are declared using union

Correct Answer: (A) Union members share the same memory, while structure members do not

14. Can a union store multiple values simultaneously?

(A) Yes
(B) No
(C) Only if they are the same type
(D) Only for floating-point types

Correct Answer: (B) No

15. Which statement is true about the following union?

                union myUnion {
                    int a;
                    float b;
                };

(A) myUnion can store both an int and a float at the same time
(B) myUnion can store either an int or a float, but not both at the same time
(C) myUnion will allocate memory for both a and b
(D) myUnion can only store an integer

Correct Answer: (B) myUnion can store either an int or a float, but not both at the same time

16. Which is the correct syntax to access a union member?

(A) union_name.member_name
(B) member_name.union_name
(C) union_name->member_name
(D) union.member_name

Correct Answer: (A) union_name.member_name

17. What is the size of the following union?

                union myUnion {
                    double d;
                    char ch[5];
                };

(A) 5 bytes
(B) 8 bytes
(C) 10 bytes
(D) 13 bytes

Correct Answer: (B) 8 bytes

18. In a union, which member is initialized last in memory?

(A) The first declared member
(B) The member assigned the last value
(C) The largest member
(D) The smallest member

Correct Answer: (B) The member assigned the last value

19. What is the correct output of the following code?

                union example {
                    int a;
                    float b;
                };
                union example ex;
                ex.a = 10;
                ex.b = 3.14;
                printf("%d", ex.a);

(A) 10
(B) 3
(C) Undefined behavior
(D) Compilation error

Correct Answer: (C) Undefined behavior

20. Which of the following operations is NOT valid for unions in C?

(A) Assigning a value to a union member
(B) Accessing union members using a dot operator
(C) Declaring a union variable
(D) Storing multiple members simultaneously

Correct Answer: (D) Storing multiple members simultaneously

5.3.2 - Nested Union.

21. What is a nested union in C?

(A) A union declared inside a structure
(B) A union declared inside another union
(C) A union declared inside a function
(D) A union with only one member

Correct Answer: (B) A union declared inside another union

22. Which keyword is used to declare a nested union?

(A) union
(B) struct
(C) typedef
(D) enum

Correct Answer: (A) union

23. In a nested union, which memory size is allocated for the union?

(A) The sum of all members' sizes
(B) The size of the largest member in the entire hierarchy
(C) Only the size of the outer union
(D) Only the size of the inner union

Correct Answer: (B) The size of the largest member in the entire hierarchy

24. What is the benefit of using nested unions in C?

(A) Allows storing multiple members simultaneously
(B) Improves memory efficiency and organizes related data
(C) Ensures faster access to union members
(D) Increases the complexity of code

Correct Answer: (B) Improves memory efficiency and organizes related data

25. Which of the following is a valid way to access a member of a nested union?

(A) outerUnion.innerUnion.member
(B) innerUnion.outerUnion.member
(C) outerUnion->innerUnion->member
(D) innerUnion.member

Correct Answer: (A) outerUnion.innerUnion.member

26. In the following code, what is the type of myUnion.innerUnion.innerChar?

                union OuterUnion {
                    int outerInt;
                    union InnerUnion {
                        char innerChar;
                        double innerDouble;
                    } innerUnion;
                };

(A) int
(B) char
(C) double
(D) float

Correct Answer: (B) char

27. What is a key difference between structures and unions in C?

(A) Unions store all members simultaneously
(B) Structures allocate memory for each member, unions allocate memory for the largest member
(C) Structures are more memory efficient than unions
(D) Unions cannot contain nested members

Correct Answer: (B) Structures allocate memory for each member, unions allocate memory for the largest member

28. How are members of a union accessed?

(A) Using the dot (.) operator
(B) Using the arrow (->) operator
(C) Using the ampersand (&) operator
(D) Using the colon (:) operator

Correct Answer: (A) Using the dot (.) operator

29. What happens if you assign a value to the outerInt and then access innerChar in the following union?

                union OuterUnion {
                    int outerInt;
                    union InnerUnion {
                        char innerChar;
                        double innerDouble;
                    } innerUnion;
                };

(A) Both values will be accessible
(B) Only innerChar will be valid
(C) Only outerInt will be valid
(D) Undefined behavior

Correct Answer: (D) Undefined behavior

30. Which of the following demonstrates the correct way to initialize a nested union?

(A) union OuterUnion myUnion = {10, {'A'}};
(B) union OuterUnion myUnion = {.outerInt = 10};
(C) union OuterUnion myUnion = {10};
(D) union OuterUnion myUnion = {A, 3.14};

Correct Answer: (B) union OuterUnion myUnion = {.outerInt = 10};

31. In the given code, which member of the outer union takes up the most memory?

                union OuterUnion {
                    int outerInt;
                    union InnerUnion {
                        char innerChar;
                        double innerDouble;
                    } innerUnion;
                };

(A) outerInt
(B) innerChar
(C) innerDouble
(D) Both innerChar and outerInt

Correct Answer: (C) innerDouble

32. Which of the following is an advantage of using unions in C?

(A) It provides direct memory access
(B) It improves memory efficiency by sharing memory among members
(C) It guarantees faster execution of programs
(D) It allows simultaneous access to all members

Correct Answer: (B) It improves memory efficiency by sharing memory among members

33. How many members of a nested union can be active at the same time?

(A) One from the outer union and one from the inner union
(B) All members
(C) Only one member at a time from either the inner or outer union
(D) Two members, one from each union

Correct Answer: (C) Only one member at a time from either the inner or outer union

34. In the following example, what will the size of OuterUnion be?

                union OuterUnion {
                    int outerInt;
                    float outerFloat;
                    union InnerUnion {
                        char innerChar;
                        double innerDouble;
                    } innerUnion;
                };

(A) 1 byte
(B) 4 bytes
(C) 8 bytes
(D) 12 bytes

Correct Answer: (C) 8 bytes

35. Which member of the nested union will be accessed in this code?

                union OuterUnion myUnion;
                myUnion.innerUnion.innerChar = 'B';
                printf("%c", myUnion.innerUnion.innerChar);

(A) outerInt
(B) outerFloat
(C) innerChar
(D) innerDouble

Correct Answer: (C) innerChar

36. What happens to the value of the outer union when you assign a value to a member of the inner union?

(A) The outer union's value remains unchanged
(B) The outer union's value is lost
(C) Both values are retained
(D) Only the outer union is valid

Correct Answer: (B) The outer union's value is lost

37. In the following code, which member is part of the inner union?

                union OuterUnion {
                    int outerInt;
                    union InnerUnion {
                        char innerChar;
                        double innerDouble;
                    } innerUnion;
                };

(A) outerInt
(B) innerChar
(C) outerFloat
(D) outerUnion

Correct Answer: (B) innerChar

38. What does the following code print?

                union OuterUnion {
                    int outerInt;
                    union InnerUnion {
                        char innerChar;
                        double innerDouble;
                    } innerUnion;
                };
                union OuterUnion myUnion;
                myUnion.innerUnion.innerDouble = 3.14;
                printf("%f", myUnion.innerUnion.innerDouble);

(A) 3.14
(B) Compilation error
(C) Undefined behavior
(D) 0.00

Correct Answer: (A) 3.14

39. How is memory allocated when a union is nested within another union?

(A) The memory for both unions is summed
(B) The largest member of both unions determines the total memory
(C) The outer union’s memory is used for the inner union
(D) Only one union uses memory

Correct Answer: (B) The largest member of both unions determines the total memory

40. Can a union be nested inside a structure in C?

(A) Yes
(B) No
(C) Only in C++
(D) Only if both are the same type

Correct Answer: (A) Yes

5.3.3 - Array of Union.

41. What is an array of unions in C?

(A) An array that stores different data types in each element
(B) An array where each element is a union that can hold different data types
(C) A union that stores an array of the same data type
(D) A union that stores different data types simultaneously

Correct Answer: (B) An array where each element is a union that can hold different data types

42. How is an array of unions declared in C?

(A) union MyUnion array[5];
(B) struct MyUnion array[5];
(C) union MyUnion[5];
(D) union MyUnion *array[5];

Correct Answer: (A) union MyUnion array[5];

43. In an array of unions, each element in the array:

(A) Can store multiple values simultaneously
(B) Shares memory with all other elements
(C) Can store one of several data types defined in the union
(D) Is always of the same data type

Correct Answer: (C) Can store one of several data types defined in the union

44. What is the memory size allocated for each element in an array of unions?

(A) The size of the smallest member in the union
(B) The size of the largest member in the union
(C) The sum of the sizes of all members in the union
(D) A fixed size determined by the array

Correct Answer: (B) The size of the largest member in the union

45. Which of the following operations is valid when using an array of unions?

(A) Accessing multiple union members at the same time
(B) Assigning values to different members in different array indices
(C) Using different data types simultaneously in the same array element
(D) Accessing union members without specifying the index

Correct Answer: (B) Assigning values to different members in different array indices

46. In the following code, what type is stored in arrayOfUnions[1]?

                union MyUnion {
                    int intValue;
                    float floatValue;
                    char charValue;
                };
                union MyUnion arrayOfUnions[5];
                arrayOfUnions[1].floatValue = 3.14;

(A) int
(B) float
(C) char
(D) Undefined behavior

Correct Answer: (B) float

47. What happens if you assign values to two members of a union at the same index in an array of unions?

(A) Both values will be stored
(B) Only the first value is retained
(C) Only the second value is retained
(D) Undefined behavior

Correct Answer: (C) Only the second value is retained

48. What is the benefit of using arrays of unions?

(A) They allow storing multiple data types in a single element of the array
(B) They provide memory efficiency by allocating space for only the largest union member
(C) They automatically check the type of each element in the array
(D) They store each member of the union at a separate memory location

Correct Answer: (B) They provide memory efficiency by allocating space for only the largest union member

49. How do you access an element of a union inside an array of unions?

(A) array[i].unionMember
(B) unionMember.array[i]
(C) array->unionMember[i]
(D) array->i.unionMember

Correct Answer: (A) array[i].unionMember

50. In the following example, what value will be printed for arrayOfUnions[2].charValue?

                union MyUnion {
                    int intValue;
                    float floatValue;
                    char charValue;
                };
                union MyUnion arrayOfUnions[5];
                arrayOfUnions[2].charValue = 'A';
                printf("%c", arrayOfUnions[2].charValue);

(A) A
(B) 0
(C) Undefined behavior
(D) Compilation error

Correct Answer: (A) A

51. Can an array of unions contain elements with different data types?

(A) Yes, each element of the array can store different types of data at different times
(B) No, all elements must store the same data type
(C) Yes, but only for integer types
(D) No, arrays cannot be used with unions

Correct Answer: (A) Yes, each element of the array can store different types of data at different times

52. Which of the following statements is true about arrays of unions?

(A) An array of unions always stores the largest member's type
(B) Only one member of the union can be used at a time in each element
(C) All members of the union can be used simultaneously in different array elements
(D) An array of unions stores the sum of the sizes of all union members

Correct Answer: (B) Only one member of the union can be used at a time in each element

53. In the following code, what is the output for items[1].price?

                union ItemAttributes {
                    int weight;
                    float price;
                    char category;
                };
                union ItemAttributes items[3];
                items[1].price = 19.99;
                printf("%.2f", items[1].price);

(A) 19.99
(B) 0.00
(C) Undefined behavior
(D) Compilation error

Correct Answer: (A) 19.99

54. How is memory allocated for arrays of unions?

(A) Each element uses the memory required by the sum of all members of the union
(B) Each element uses the memory required by the largest member of the union
(C) Memory is allocated only for the first element
(D) Memory allocation is dynamic based on the number of elements in use

Correct Answer: (B) Each element uses the memory required by the largest member of the union

55. Can arrays of unions be passed as function arguments?

(A) Yes, arrays of unions can be passed to functions like any other array
(B) No, arrays of unions cannot be passed to functions
(C) Yes, but only if they contain integer types
(D) Yes, but only by reference

Correct Answer: (A) Yes, arrays of unions can be passed to functions like any other array

56. What would happen if you try to print an uninitialized element of an array of unions?

(A) It will print a garbage value
(B) It will print 0
(C) Undefined behavior
(D) Compilation error

Correct Answer: (C) Undefined behavior

57. Which of the following correctly initializes an element in an array of unions?

(A) array[0] = {10};
(B) array[0].intValue = 10;
(C) array[0] = {.intValue = 10};
(D) array[0] = intValue = 10;

Correct Answer: (B) array[0].intValue = 10;

58. In an array of unions, each element is initialized:

(A) Automatically to the first member of the union
(B) Manually for each member
(C) Using the size of the smallest member
(D) Automatically to zero

Correct Answer: (B) Manually for each member

59. Can arrays of unions be dynamically allocated?

(A) Yes, using malloc
(B) No, arrays of unions must be statically allocated
(C) Only in C++
(D) Only if the array contains more than 5 elements

Correct Answer: (A) Yes, using malloc

60. What is a key difference between arrays of unions and arrays of structures?

(A) Arrays of unions store all members simultaneously
(B) Arrays of unions allocate memory based on the largest member, arrays of structures allocate memory for all members
(C) Arrays of structures cannot store different data types
(D) Arrays of structures are faster to access

Correct Answer: (B) Arrays of unions allocate memory based on the largest member, arrays of structures allocate memory for all members

5.3.4 - Passing Union as Arguments in Functions.

61. How can you pass a union to a function in C?

(A) By passing the entire union
(B) By passing specific union members
(C) By passing a pointer to the union
(D) All of the above

Correct Answer: (D) All of the above

62. What happens when you pass a union by value to a function?

(A) The original union is modified
(B) A copy of the union is passed, and the original remains unchanged
(C) The function accesses the union directly
(D) The union is passed as a pointer

Correct Answer: (B) A copy of the union is passed, and the original remains unchanged

63. What is the syntax to pass a specific member of a union to a function?

(A) functionName(union.member);
(B) functionName(&union.member);
(C) functionName(*union.member);
(D) functionName.union.member;

Correct Answer: (A) functionName(union.member);

64. Why would you pass a union by reference to a function?

(A) To modify the original union in the calling function
(B) To save memory
(C) To prevent the union from being copied
(D) All of the above

Correct Answer: (D) All of the above

65. Which operator is used to access members of a union when passed as a pointer to a function?

(A) . (dot operator)
(B) * (dereference operator)
(C) -> (arrow operator)
(D) & (address operator)

Correct Answer: (C) -> (arrow operator)

66. What is the result of passing a union pointer to a function?

(A) The function works with a copy of the union
(B) The original union can be modified
(C) The union is passed by value
(D) The function can only read the union

Correct Answer: (B) The original union can be modified

67. How can you ensure type safety when passing union members to a function?

(A) By always passing the entire union
(B) By specifying the correct data type in the function argument
(C) By using type casting in the function
(D) Type safety is automatic in unions

Correct Answer: (B) By specifying the correct data type in the function argument

68. What happens if you pass the wrong union member type to a function?

(A) Compilation error
(B) Unpredictable behavior
(C) The program will automatically cast it
(D) The function will print a warning

Correct Answer: (B) Unpredictable behavior

69. How is memory handled when passing a union by value to a function?

(A) The function accesses the original memory location
(B) A new memory location is created for the union copy
(C) The union is passed by reference
(D) The union is passed as a pointer

Correct Answer: (B) A new memory location is created for the union copy

70. Which of the following is a valid function signature for passing a union by reference?

(A) void function(union MyUnion u);
(B) void function(union MyUnion *u);
(C) void function(&union MyUnion u);
(D) void function(*union MyUnion u);

Correct Answer: (B) void function(union MyUnion *u);

71. When passing a union pointer to a function, how can you modify a member of the union?

(A) By using the . (dot) operator
(B) By using the -> (arrow) operator
(C) By using the * (dereference) operator
(D) By using the & (address) operator

Correct Answer: (B) By using the -> (arrow) operator

72. What is the benefit of passing specific union members rather than the entire union?

(A) It saves memory and improves performance
(B) It allows the function to access all union members
(C) It prevents modifications to the original union
(D) It simplifies type checking

Correct Answer: (A) It saves memory and improves performance

73. Which of the following is true about passing unions by value to a function?

(A) The union is modified within the function
(B) The original union remains unchanged after the function call
(C) The union is automatically passed by reference
(D) The union is copied only if it's a large union

Correct Answer: (B) The original union remains unchanged after the function call

74. How do you pass a union as an argument to a function if you want to avoid copying the union?

(A) Pass a pointer to the union
(B) Use the & operator to pass by reference
(C) Pass only specific union members
(D) Both A and B

Correct Answer: (D) Both A and B

75. Which keyword is used to define a union in C?

(A) struct
(B) class
(C) union
(D) enum

Correct Answer: (C) union

76. What is the primary difference between passing a structure and a union to a function?

(A) A union stores only one value at a time, while a structure stores all its members
(B) A union uses less memory
(C) A structure passes all its members, while a union passes only the largest member
(D) Both pass their members the same way

Correct Answer: (A) A union stores only one value at a time, while a structure stores all its members

77. How do you pass multiple members of a union to a function at the same time?

(A) Pass the union itself by reference
(B) Pass a structure that contains the union
(C) Pass each member individually
(D) Unions cannot pass multiple members simultaneously

Correct Answer: (D) Unions cannot pass multiple members simultaneously

78. What is a possible drawback of passing union members to a function?

(A) Loss of flexibility in the function
(B) Loss of type safety
(C) The union may be modified unexpectedly
(D) It can result in memory leaks

Correct Answer: (B) Loss of type safety

79. How can you prevent modification of a union passed to a function?

(A) Pass the union by value
(B) Pass the union by reference
(C) Pass a constant pointer to the union
(D) Use a const union

Correct Answer: (C) Pass a constant pointer to the union

80. What happens when a union is passed by reference to a function?

(A) The function receives a copy of the union
(B) The function works directly on the original union
(C) The union is passed as a value
(D) Only specific members are passed

Correct Answer: (B) The function works directly on the original union