Structures, Unions, Enums Questions and Answers

Q: #include <stdio.h> typedef enum{ Male, Female=-1 }SEX; int main() { SEX var = Male; SEX var1 = Female; printf("%d %d",var, var1); return 0; }

Correct answer: 0 -1Male takes the default first value, 0, and Female is then explicitly set to -1. Explicit values may be given in any order and may be negative - the compiler only fills in the ones you leave out, continuing from the last value given.

Q: Which of the following are themselves a collection of different data types?

Correct answer: StructuresA structure groups members of different types under one name - an int, a float and a character array together. An array requires every element to be the same type, and a string is an array of characters.

Q: A user-defined data type can be created with ___________

Correct answer: all of the mentionedAll three create user-defined types. struct aggregates members of different types; enum names a set of integer constants; and typedef gives a new name to an existing type, which is how struct node * becomes NODEPTR. A union belongs on the same list.

Q: Which operator connects the structure name to its member name?

Correct answer: .The dot connects a structure variable to its member: s.member. Through a pointer the arrow is used instead, p->member, which is shorthand for (*p).member.

Q: Which of the following cannot be a structure member?

Correct answer: FunctionA structure member must be an object with storage, and a function is not - so a function cannot be a member of a C structure. What can be a member is a pointer to a function, which is how C programs implement dispatch tables and something resembling methods. Arrays and nested structures are ordinary members.

Q: Which of the following structure declarations will throw an error?

Correct answer: struct temp s; struct temp{}; main(){}This one is an error. Declaring struct temp s; before the structure has been defined means declaring an object of an incomplete type - the compiler does not yet know how much storage to reserve. The other two are fine: the first defines the type and a variable together, and the second defines the type before using it. (A pointer to an incomplete type would be legal, since a pointer’s size is known.)

Q: What is the output of this C code? #include <stdio.h> struct student { int no; char name[20]; } void main() { struct student s; s.no = 8; printf("hello"); }

Correct answer: Compile time errorThe structure definition is missing its terminating semicolon after the closing brace. Without it the compiler reads on and tries to make sense of void main() as part of the declaration, and the program fails to compile.

Q: What will be the output of the program if it is executed like below? cmd> sample /* sample.c */ #include <stdio.h> int main(int argc, char **argv) { printf("%s\n", argv[argc-1]); return 0; }

Correct answer: sampleargv[0] is the program name as invoked, and with no further arguments argc is 1 - so argv[argc-1] is argv[0], which prints sample. The array always has argc entries plus a null pointer at argv[argc].

101.

#include <stdio.h>

typedef enum{
    Male, Female=-1
}SEX;

int main()
{
  SEX var = Male;
  SEX var1 = Female;
  printf("%d %d",var, var1);
  return 0;
}

A.Compilation Error
B.Garbage Value 0
C.-1 -1
D.0 -1

Answer: D

Correct answer: 0 -1

Male takes the default first value, 0, and Female is then explicitly set to -1. Explicit values may be given in any order and may be negative - the compiler only fills in the ones you leave out, continuing from the last value given.

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102.

Which of the following are themselves a collection of different data types?

A.string
B.structures
C.char
D.all of the mentioned

Answer: B

Correct answer: Structures

A structure groups members of different types under one name - an int, a float and a character array together. An array requires every element to be the same type, and a string is an array of characters.

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103.

A user-defined data type can be created with ___________

A.struct
B.enum
C.typedef
D.all of the mentioned

Answer: D

Correct answer: all of the mentioned

All three create user-defined types. struct aggregates members of different types; enum names a set of integer constants; and typedef gives a new name to an existing type, which is how struct node * becomes NODEPTR. A union belongs on the same list.

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104.

Which operator connects the structure name to its member name?

A.-
B.<-
C..
D.Both <- and .

Answer: C

Correct answer: .

The dot connects a structure variable to its member: s.member. Through a pointer the arrow is used instead, p->member, which is shorthand for (*p).member.

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105.

Which of the following cannot be a structure member?

A.Another structure
B.Function
C.Array
D.None of the mentioned

Answer: B

Correct answer: Function

A structure member must be an object with storage, and a function is not - so a function cannot be a member of a C structure. What can be a member is a pointer to a function, which is how C programs implement dispatch tables and something resembling methods. Arrays and nested structures are ordinary members.

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106.

Which of the following structure declarations will throw an error?

A.struct temp{}s; main(){}
B.struct temp{}; struct temp s; main(){}
C.struct temp s; struct temp{}; main(){}
D.None of the mentioned

Answer: D

Correct answer: struct temp s; struct temp{}; main(){}

This one is an error. Declaring struct temp s; before the structure has been defined means declaring an object of an incomplete type - the compiler does not yet know how much storage to reserve. The other two are fine: the first defines the type and a variable together, and the second defines the type before using it. (A pointer to an incomplete type would be legal, since a pointer’s size is known.)

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107.

What is the output of this C code?

#include <stdio.h>
    struct student
    {
        int no;
        char name[20];
    }
    void main()
    {
        struct student s;
        s.no = 8;
        printf("hello");
    }

A.Compile time error
B.Nothing
C.hello
D.Varies

Answer: A

Correct answer: Compile time error

The structure definition is missing its terminating semicolon after the closing brace. Without it the compiler reads on and tries to make sense of void main() as part of the declaration, and the program fails to compile.

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108.

What will be the output of the program if it is executed like below?
cmd> sample

/* sample.c */
#include <stdio.h>

int main(int argc, char **argv)
{
    printf("%s\n", argv[argc-1]);
    return 0;
}

A.sample
B.samp
C.No output

Answer: A

Correct answer: sample

argv[0] is the program name as invoked, and with no further arguments argc is 1 - so argv[argc-1] is argv[0], which prints sample. The array always has argc entries plus a null pointer at argv[argc].

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