Members of a union are accessed as ________________
Answer: C
Correct answer: Both a & b
A union member is reached exactly as a structure member is: with the dot through a variable (u.member) and with the arrow through a pointer (p->member). The syntax is identical; only the storage layout differs.
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The number of distinct nodes the following struct declaration can point to is
struct node
{
struct node *left;
struct node *centre;
struct node *right;
};
Answer: A
Correct answer: All of the above
The structure holds three pointers, so at most it points to three nodes - but nothing requires them to be different. Two of the pointers may hold the same address, or all three may, so the number of distinct nodes reached may be 1, 2 or 3. All the counts offered are possible.
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#include <stdio.h>
typedef enum{
Male, Female=-1
}SEX;
int main()
{
SEX var = Male;
SEX var1 = Female;
printf("%d %d",var, var1);
return 0;
}
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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Which of the following accesses a variable in structure b?
Answer: B
Correct answer: b.var;
b is a structure variable, so its members are reached with the dot: b.var. The arrow is for pointers.
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What is the output of this program?
#include <stdio.h>
int main()
{
union demo {
int x;
int y;
};
union demo a = 100;
printf("%d %d",a.x,a.y);
}
Answer: D
Correct answer: Compilation Error
A union cannot be initialised from a bare value: union demo a = 100; is rejected, because the compiler must be told which member is meant. union demo a = {100}; would initialise the first member, and {.y = 100} would name it explicitly.
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What is the output of this program?
#include <stdio.h>
void main()
{
struct number
{
int no;
char name[20];
};
struct number s;
s.no = 50;
printf("%d", s.no);
}
Answer: D
Correct answer: 50
Declaring the structure type inside a function is legal - it is simply local to that block. The member is set and printed, giving 50.
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Is the size of a union the size of its largest member?
Answer: A
Correct answer: Yes
A union’s members all occupy the same storage, so its size is that of its largest member - enough to hold whichever one is in use. A structure, by contrast, gives every member its own space and so is at least the sum of them.
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It is not possible to create an array of pointer to structures.
Answer: B
Correct answer: FALSE
An array of pointers to structures is perfectly ordinary - struct node *arr[10]; - and it is common, because swapping pointers is far cheaper than copying whole structures. So the statement that it is impossible is false.
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Which of the following structure declarations will throw an error?
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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The following C declarations
struct node
{
int i;
float j;
};
struct node *s[10] ;
define s to be
Answer: A
Correct answer: An array, each element of which is a pointer to a structure of type node
Subscript binds tighter than the dereference, so struct node *s[10] groups as struct node *(s[10]) - an array of 10 pointers, each to a struct node. A pointer to an array would need parentheses in the other place: struct node (*s)[10].
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