Interview Questions and Answers in C - Declarations - Agilent, Akamai, Alcatel

This section on C interview questions and answers focuses on “Declarations”. One shall practice these interview questions to improve their C programming skills needed for various interviews (campus interviews, walk-in 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 the detailed explanation of the answers which helps in better understanding of C concepts.

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

1. What is the output of this C code?

```
    #include <stdio.h>
```
```
    void foo(const int *);
```
```
    int main()
```
```
    {
```
```
        const int i = 10;
```
```
        printf("%d ", i);
```
```
        foo(&i);
```
```
        printf("%d", i);
```
```
 
```
```
    }
```
```
    void foo(const int *i)
```
```
    {
```
```
        *i = 20;
```
```
    }
```

a) Compile time error
b) 10 20
c) Undefined value
d) 10
View Answer

Answer: a
Explanation: Cannot change a const type value.
Output:
$ cc pgm1.c
pgm1.c: In function ‘foo’:
pgm1.c:13: error: assignment of read-only location ‘*i’

2. Comment on the output of this C code?

```
    #include <stdio.h>
```
```
    int main()
```
```
    {
```
```
        const int i = 10;
```
```
        int *ptr = &i;
```
```
        *ptr = 20;
```
```
        printf("%d\n", i);
```
```
        return 0;
```
```
    }
```

a) Compile time error
b) Compile time warning and printf displays 20
c) Undefined behaviour
d) 10
View Answer

Answer: b
Explanation: Changing const variable through non-constant pointers invokes compiler warning.
Output:
$ cc pgm2.c
pgm2.c: In function ‘main’:
pgm2.c:5: warning: initialization discards qualifiers from pointer target type
$ a.out
20

3. What is the output of this C code?

```
    #include <stdio.h>
```
```
    int main()
```
```
    {
```
```
        j = 10;
```
```
        printf("%d\n", j++);
```
```
        return 0;
```
```
    }
```

a) 10
b) 11
c) Compile time error
d) 0
View Answer

Answer: c
Explanation: Variable j is not defined.
Output:
$ cc pgm3.c
pgm3.c: In function ‘main’:
pgm3.c:4: error: ‘j’ undeclared (first use in this function)
pgm3.c:4: error: (Each undeclared identifier is reported only once
pgm3.c:4: error: for each function it appears in.)

4. Does this compile without error?

```
    #include <stdio.h>
```
```
    int main()
```
```
    {
```
```
        for (int k = 0; k < 10; k++);
```
```
            return 0;
```
```
    }
```

a) Yes
b) No
c) Depends on the C standard implemented by compilers
d) None of the mentioned
View Answer

Answer: c
Explanation: Compilers implementing C90 do not allow this, but compilers implementing C99 allow it.
Output:
$ cc pgm4.c
pgm4.c: In function ‘main’:
pgm4.c:4: error: ‘for’ loop initial declarations are only allowed in C99 mode
pgm4.c:4: note: use option -std=c99 or -std=gnu99 to compile your code

5. Does this compile without error?

```
    #include <stdio.h>
```
```
    int main()
```
```
    {
```
```
        int k;
```
```
        {
```
```
            int k;
```
```
            for (k = 0; k < 10; k++);
```
```
        }
```
```
    }
```

a) Yes
b) No
c) Depends on the compiler
d) Depends on the C standard implemented by compilers
View Answer

Answer: a
Explanation: There can be blocks inside the block. But within block variables have only block scope.
Output:
$ cc pgm5.c

6. Which of the following declaration is not supported by C?
a) String str;
b) char *str;
c) float str = 3e2;
d) Both String str; & float str = 3e2;
View Answer

Answer: a
Explanation: String str; is legal in Java, but not in C.

```
    #include <stdio.h>
```
```
    int main()
```
```
    {
```

        char *var = "Advanced Training in C by Sanfoundry.com";

```
    }
```

Which of the following format identifier can never be used for the variable var?
a) %f
b) %d
c) %c
d) %s
View Answer

Answer: a
Explanation: %c can be used to print the indexed position. %d can still be used to display its ASCII value. %s is recommended.
%f cannot be used for the variable var.

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