C++ Declaration Questions and Answers

This section on C++ interview questions and answers focuses on “Declaration”. 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 “Declaration” along with answers, explanations and/or solutions:

1. Choose the correct option.

    extern int i;
    int i;

a) both 1 and 2 declare i
b) 1 declares the variable i and 2 defines i
c) 1 declares and defines i, 2 declares i
d) 1 declares i,2 declares and defines i
View Answer

Answer: d
Explanation: The keyword extern is not a definition and is not allocated storage until it is initialized.

2. Pick the right option.

Statement 1: A definition is also a declaration.
Statement 2: An identifier can be declared just once.

a) Statement 1 is true, Statement 2 is false
b) Statement 2 is true, Statement 1 is false
c) Both are false
d) Both are true
View Answer

Answer: a
Explanation: When we define a variable, we automatically declare its type and assigns a memory location for it. So, statement1 is true. An identifier can be declared many times as long as they have different scopes. So, statement2 is false.

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3. Which of the given statements are false?

i. extern int func;
ii. extern int func2(int,int);
iii. int func2(int,int);
iv. extern class foo;

a) iii and iv only
b) ii and iii only
c) only iv
d) ii, iii and iv
View Answer

Answer: c
Explanation: No extern are allowed for class declarations.

4. Pick the right option.

Statement 1: Global values are not initialized by the stream.
Statement 2: Local values are implicitly initialised to 0.

a) Statement 1 is true, Statement 2 is false
b) Statement 2 is true, Statement 1 is false
c) Both are false
d) Both are true
View Answer

Answer: c
Explanation: Global values are implicitly initialised to 0, but local values have to be initialised by the system.

5. What will be the output of the following C++ code?

```
    #include <iostream>
```
```
    using namespace std;
```
```
    int g = 100;
```
```
    int main()
```
```
    {
```
```
        int a;
```
```
        {
```
```
            int b;
```
```
            b = 20;
```
```
            a = 35;
```
```
            g = 65;
```
```
           cout << b << a << g;
```
```
        }
```
```
        a = 50;
```
```
        cout << a << g;
```
```
        return 0;
```
```
    }
```

a) 2035655065
b) 2035655035
c) 2035635065
d) 2035645065
View Answer

Answer: a
Explanation: The local values of a and g within the block are more dominant than the global values.
Output:
$ g++ dec1.cpp
$ a.out
2035655065

6. Can two functions declare variables(non static) with the same name?
a) No
b) Yes
c) Yes, but not a very efficient way to write programs
d) No, it gives a runtime error
View Answer

Answer: c
Explanation: We can declare variables with the same name in two functions because their scope lies within the function.

7. What will be the output of the following C++ code?

```
    #include <iostream>
```
```
    using namespace std;
```
```
    void addprint()
```
```
    {
```
```
        static int s = 1;
```
```
        s++;
```
```
        cout << s;
```
```
    }
```
```
    int main()
```
```
    {
```
```
        addprint();
```
```
        addprint();
```
```
        addprint();
```
```
        return 0;
```
```
    }
```

a) 234
b) 111
c) 123
d) 235
View Answer

Answer: a
Explanation: The variable that is declared as static has a file scope.
Output:

$ g++ dec2.cpp
$ a.out
234

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

```
    #include <iostream>
```
```
    using namespace std;
```
```
    int main()
```
```
    {
```
```
        int a = 10;
```
```
        if (a < 10) 
```
```
        {
```
```
            for (i = 0; i < 10; i++)
```
```
               cout << i;
```
```
        }
```
```
        else 
```
```
        {
```
```
            cout << i;
```
```
        }
```
```
        return 0;
```
```
    }
```

a) 0123456789
b) 123456789
c) 0
d) error
View Answer

Answer: d
Explanation: We will get compilation error because ‘i’ is an undeclared identifier.

9. Identify the incorrect statements.

    int var = 10;
    int *ptr = &(var + 1); //statement 1
    int *ptr2 = &var; //statement 2
    &&var = 40; //statement 3

a) Statement 1 and 2 are wrong
b) Statement 2 and 3 are wrong
c) Statement 1 and 3 are wrong
d) Statement 1, 2 and 3 are wrong
View Answer

Answer: c
Explanation: In statement 1 lvalue is required as unary ‘&’ operand and in statement 3 lvalue is required as left operand.

10. Identify the type of variables.

    typedef char* CHAR;
    CHAR p,q;

a) char*
b) char
c) CHAR
d) unknown
View Answer

Answer: a
Explanation: The statement makes CHAR a synonym for char*.

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