Structures, Unions, Enums Questions and Answers

Q: What is the output of this program? #include <stdio.h> int main() { enum days {MON=-1, TUE, WED=4, THU, FRI, SAT}; printf("%d, %d, %d, %d, %d, %d", MON, TUE, WED, THU, FRI, SAT); return 0; }

Correct answer: -1 0 4 5 6 7Enumerators continue from the last value given. MON is set to -1, so TUE is 0; WED is set to 4, so THU, FRI and SAT are 5, 6, 7. Values may be repeated or given out of order - the compiler only fills in what you leave out.

Q: Predict the output of following C program #include <stdio.h> struct Point { int x, y, z; }; int main() { struct Point p1 = {.y = 0, .z = 1, .x = 2}; printf("%d %d %d", p1.x, p1.y, p1.z); return 0; }

Correct answer: 2 0 1These are designated initialisers, introduced in C99: each value names the member it initialises, so their order in the braces is irrelevant. .x = 2, .y = 0, .z = 1 whatever order they are written in, and the program prints 2 0 1.

Q: What will be the output of the following C code? #include <stdio.h> enum sanfoundry { a,b,c=5 }; int main() { enum sanfoundry s; b=10; printf("%d",b); }

Correct answer: Errorb is an enumerator - a constant - so b = 10; is an assignment to something that is not an lvalue, and the compiler rejects it. Only an enum variable can be assigned to.

Q: What will be the output of the following C code? #include <stdio.h> enum sanfoundry { a=1,b,c,d,e }; int main() { printf("%d",b*c+e-d); }

Correct answer: 7Values run on from the one given: a = 1, so b = 2, c = 3, d = 4, e = 5. Then\[ b \times c + e - d = 2 \times 3 + 5 - 4 = 7 \]

Q: What is the correct syntax to declare a function foo() which receives an array of structure in function?

Correct answer: void foo(struct *var);An array argument decays to a pointer to its first element, so a function receiving an array of structures takes a pointer to structure. (In real code the tag must be named - void foo(struct tagname *var); - since struct alone is not a type.) Passing an array never copies it, so the length must be passed separately.

Q: What will be the output of the following C code? main() { enum resut {pass, fail}; enum result s1,s2; s1=pass; s2=fail; printf("%d",s1); }

Correct answer: errorThe enumeration is declared as enum resut - a typo - and the variables are then declared as enum result, a tag that does not exist. The compiler reports an incomplete type.

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

Correct answer: .The dot operator selects a member of a structure variable: s.member. The arrow -> does the same through a pointer, and is exactly equivalent to (*p).member.

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

Correct answer: Runtime error (Segmentation fault)%s tells printf to treat its argument as a pointer to a string, but the arguments are the integers 0 and 1. printf then dereferences address 0 and address 1, and the program is killed. Nothing in the program remembers the names Male and Female - printing them requires an array of strings indexed by the enumerator.

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.

91.

What is the output of this program?

#include <stdio.h>
int main()
{
    enum days {MON=-1, TUE, WED=4, THU, FRI, SAT};
    printf("%d, %d, %d, %d, %d, %d", MON, TUE, WED, THU, FRI, SAT);
    return 0;
}

A.-1 0 4 5 6 7
B.-1 0 1 2 3 4
C.0 1 2 3 4 5
D.Error

Answer: A

Correct answer: -1 0 4 5 6 7

Enumerators continue from the last value given. MON is set to -1, so TUE is 0; WED is set to 4, so THU, FRI and SAT are 5, 6, 7. Values may be repeated or given out of order - the compiler only fills in what you leave out.

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92.

Predict the output of following C program

#include <stdio.h>
struct Point
{
  int x, y, z;
};
 
int main()
{
  struct Point p1 = {.y = 0, .z = 1, .x = 2};
  printf("%d %d %d", p1.x, p1.y, p1.z);
  return 0;
}

A.Compiler Error
B.2 0 1
C.0 1 2
D.2 1 0

Answer: B

Correct answer: 2 0 1

These are designated initialisers, introduced in C99: each value names the member it initialises, so their order in the braces is irrelevant. .x = 2, .y = 0, .z = 1 whatever order they are written in, and the program prints 2 0 1.

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93.

What will be the output of the following C code?

#include <stdio.h>
enum sanfoundry
{
    a,b,c=5
};
int main()
{
    enum sanfoundry s;
    b=10;
    printf("%d",b);
}

A.Error
B.10
C.1
D.4

Answer: A

Correct answer: Error

b is an enumerator - a constant - so b = 10; is an assignment to something that is not an lvalue, and the compiler rejects it. Only an enum variable can be assigned to.

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94.

What will be the output of the following C code?

#include <stdio.h>
enum sanfoundry
{
    a=1,b,c,d,e
};
int main()
{
    printf("%d",b*c+e-d);
}

A.Error
B.7
C.2
D.4

Answer: B

Correct answer: 7

Values run on from the one given: a = 1, so b = 2, c = 3, d = 4, e = 5. Then

\[ b \times c + e - d = 2 \times 3 + 5 - 4 = 7 \]

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95.

What is the correct syntax to declare a function foo() which receives an array of structure in function?

A.void foo(struct *var);
B.void foo(struct *var[]);
C.void foo(struct var);
D.none of the mentioned

Answer: A

Correct answer: void foo(struct *var);

An array argument decays to a pointer to its first element, so a function receiving an array of structures takes a pointer to structure. (In real code the tag must be named - void foo(struct tagname *var); - since struct alone is not a type.) Passing an array never copies it, so the length must be passed separately.

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96.

What will be the output of the following C code?

main()
{
    enum resut {pass, fail};
    enum result s1,s2;
    s1=pass;
    s2=fail;
    printf("%d",s1);
}

A.error
B.pass
C.fail

Answer: A

Correct answer: error

The enumeration is declared as enum resut - a typo - and the variables are then declared as enum result, a tag that does not exist. The compiler reports an incomplete type.

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97.

Which operator connects the structure name to its member name?

A.-
B.->
C..
D.both . and ->

Answer: C

Correct answer: .

The dot operator selects a member of a structure variable: s.member. The arrow -> does the same through a pointer, and is exactly equivalent to (*p).member.

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98.

#include <stdio.h>

typedef enum{
    Male, Female
}SEX;

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

A.Male Female
B.0 1
C.Runtime error (Segmentation fault)
D.Compilation Error: Can't cast

Answer: C

Correct answer: Runtime error (Segmentation fault)

%s tells printf to treat its argument as a pointer to a string, but the arguments are the integers 0 and 1. printf then dereferences address 0 and address 1, and the program is killed. Nothing in the program remembers the names Male and Female - printing them requires an array of strings indexed by the enumerator.

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99.

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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100.

What will be output for the following code?

A.error
B.success
C.failure

Answer: A

The code shown above results in an error, stating : storage size of t1 and t2 unknown. There is an error in the declaration of these variables in the statement: enum test1 t1,t2;

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