250+ TOP MCQs on Unions and Answers [2024]

C Objective Questions on “Unions”. One shall practice these Objective Questions to improve their C programming skills needed for various interviews (campus interviews, walkin interviews, company interviews), placements, entrance exams and other competitive exams. These questions can be attempted by anyone focusing on learning C Programming language. They can be a beginner, fresher, engineering graduate or an experienced IT professional. Our C Objective Questions come with detailed explanation of the answers which helps in better understanding of C concepts.

Here is a listing of C Objective Questions on “Unions” along with answers, explanations and/or solutions:

1. The size of a union is determined by the size of the __________
a) First member in the union
b) Last member in the union
c) Biggest member in the union
d) Sum of the sizes of all members
Answer: c
Clarification: None.

2. Which member of the union will be active after REF LINE in the following C code?

```
    #include 
```
```
    union temp
```
```
    {
```
```
        int a;
```
```
        float b;
```
```
        char c;
```
```
    };
```

    union temp s = {1,2.5,’A’}; //REF LINE

a) a
b) b
c) c
d) Such declaration are illegal
Answer: a
Clarification: None.

3. What would be the size of the following union declaration? (Assuming size of double = 8, size of int = 4, size of char = 1)

```
    #include 
```
```
    union uTemp
```
```
    {
```
```
        double a;
```
```
        int b[10];
```
```
        char c;
```
```
    }u;
```

a) 4
b) 8
c) 40
d) 80
Answer: c
Clarification: None.

4. What type of data is holded by variable u int in the following C code?

```
    #include 
```
```
    union u_tag
```
```
    {
```
```
        int ival;
```
```
        float fval;
```
```
        char *sval;
```
```
    } u;
```

a) Will be large enough to hold the largest of the three types;
b) Will be large enough to hold the smallest of the three types;
c) Will be large enough to hold the all of the three types;
d) None of the mentioned
Answer: a
Clarification: None.

5. Members of a union are accessed as________________
a) union-name.member
b) union-pointer->member
c) both union-name.member & union-pointer->member
d) none of the mentioned
Answer: c
Clarification: None.

6. In the following C code, we can access the 1st character of the string sval by using _______

```
    #include 
```
```
    struct
```
```
    {
```
```
        char *name;
```
```
        union
```
```
        {
```
```
            char *sval;
```
```
        } u;
```
```
    } symtab[10];
```

a) *symtab[i].u.sval
b) symtab[i].u.sval[0].
c) You cannot have union inside structure
d) Both *symtab[i].u.sval & symtab[i].u.sval[0].
Answer: d
Clarification: None.

7. What will be the output of the following C code (Assuming size of int and float is 4)?

```
    #include 
```
```
    union
```
```
    {
```
```
        int ival;
```
```
        float fval;
```
```
    } u;
```
```
    void main()
```
```
    {
```
```
        printf("%d", sizeof(u));
```
```
    }
```

a) 16
b) 8
c) 4
d) 32
Answer: c
Clarification: None.

8. What will be the output of the following C code?

```
    #include 
```
```
    union stu
```
```
    {
```
```
        int ival;
```
```
        float fval;
```
```
    };
```
```
    void main()
```
```
    {
```
```
        union stu r;
```
```
        r.ival = 5;
```
```
        printf("%d", r.ival);
```
```
    }
```

a) 9
b) Compile time error
c) 16
d) 5
Answer: d
Clarification: None.

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