C Interview Questions - Unions - Rockwell, Roxar, RSA

This section on C interview questions and answers focuses on “Unions”. One shall practice these interview 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 Interview questions come with detailed explanation of the answers which helps in better understanding of C concepts.

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

1. What is the output of this C code?

```
    #include <stdio.h>
```
```
    union
```
```
    {
```
```
        int x;
```
```
        char y;
```
```
    }p;
```
```
    int main()
```
```
    {
```
```
        p.x = 10;
```
```
        printf("%d\n", sizeof(p));
```
```
    }
```

a) Compile time error
b) sizeof(int) + sizeof(char)
c) Depends on the compiler
d) sizeof(int)
View Answer

Answer: d
Explanation: None.

2. What is the output of this C code?

```
    #include <stdio.h>
```
```
    union
```
```
    {
```
```
        int x;
```
```
        char y;
```
```
    }p;
```
```
    int main()
```
```
    {
```
```
        p.y = 60;
```
```
        printf("%d\n", sizeof(p));
```
```
    }
```

a) Compile time error
b) sizeof(int) + sizeof(char)
c) Depends on the compiler
d) sizeof(char)
View Answer

Answer: c
Explanation: None.

3. What is the output of this C code?

```
    #include <stdio.h>
```
```
    union p
```
```
    {
```
```
        int x;
```
```
        char y;
```
```
    };
```
```
    int main()
```
```
    {
```
```
        union p p, b;
```
```
        p.y = 60;
```
```
        b.x = 12;
```
```
        printf("%d\n", p.y);
```
```
    }
```

a) Compile time error
b) Depends on the compiler
c) 60
d) Undefined behaviour
View Answer

Answer: c
Explanation: None.

4. What is the output of this C code?

```
    #include <stdio.h>
```
```
    union p
```
```
    {
```
```
        int x;
```
```
        char y;
```
```
    }k = {1, 97};
```
```
    int main()
```
```
    {
```
```
        printf("%d\n", k.y);
```
```
    }
```

a) Compile time error
b) 97
c) a
d) 1
View Answer

Answer: d
Explanation: None.

5. What is the output of this C code?

```
    #include <stdio.h>
```
```
    union p
```
```
    {
```
```
        int x;
```
```
        char y;
```
```
    }k = {.y = 97};
```
```
    int main()
```
```
    {
```
```
        printf("%d\n", k.y);
```
```
    }
```

a) Compile time error
b) 97
c) a
d) Depends on the standard
View Answer

Answer: b
Explanation: None.

6. What is the output of this C code?

```
    #include <stdio.h>
```
```
    union p
```
```
    {
```
```
        int x;
```
```
        float y;
```
```
    };
```
```
    int main()
```
```
    {
```
```
        union p p, b;
```
```
        p.x = 10;
```
```
        printf("%f\n", p.y);
```
```
    }
```

a) Compile time error
b) Implementation dependent
C) 10.000000
d) 0.000000
View Answer

Answer: b
Explanation: None.

7. Which of the following share a similarity in syntax?

1. Union, 2. Structure, 3. Arrays and 4. Pointers

a) 3 and 4
b) 1 and 2
c) 1 and 3
d) 1, 3 and 4
View Answer

Answer: b
Explanation: None.

8. What is the output of this C code?

```
    #include <stdio.h>
```
```
    union utemp
```
```
    {
```
```
        int a;
```
```
        double b;
```
```
        char c;
```
```
    }u;
```
```
    int main()
```
```
    {
```
```
        u.c = 'A';
```
```
        u.a = 1;
```
```
        printf("%d", sizeof(u));
```
```
    }
```

The output will be: (Assuming size of char = 1, int = 4, double = 8)
a) 1
b) 4
c) 8
d) 13
View Answer

Answer: c
Explanation: None.

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