Random Numbers - C++ Questions and Answers

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

1. Which header file is used to create the pseudo random generator?
a) random
b) cstdlib
c) rand
d) both random and cstdlib
View Answer

Answer: d
Explanation: cstdlib header file is used to create pseudo random number. C++11 standard added random header file as well to generate random numbers.

2. Which is a constant defined in <cstdlib> header file?
a) RAND_MAX
b) Rand
c) Srand
d) Blitz
View Answer

Answer: a
Explanation: RAND_MAX is a constant defined in <cstdlib> for deciding the maximum random number that can be produced.

3. How many parameters are available in srand function?
a) 1
b) 2
c) 3
d) 4
View Answer

Answer: a
Explanation: There is one parameter available in srand function. That is an integer value to be used as seed by the pseudo-random number generator algorithm.

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

```
    #include <cstdlib>
```
```
    #include <iostream>
```
```
    using namespace std;
```
```
    int main()
```
```
    {
```
```
        int ran = rand();
```
```
        cout << ran << endl;
```
```
    }
```

a) Any number
b) 89
c) 0 to RAND_MAX
d) 79
View Answer

Answer: c
Explanation: As the declared number is integer, It will produce the random number from 0 to RAND_MAX. The value of RAND_MAX is library-dependent, but is guaranteed to be at least 32767 on any standard library implementation.
Output:

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$ g++ rand.cpp
$ a.out
574

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

```
    #include <cstdlib>
```
```
    #include <iostream>
```
```
    using namespace std;
```
```
    int main()
```
```
    {
```
```
        cout << RAND_MAX << endl;
```
```
    }
```

a) 4385234
b) 12321412
c) Depends on the compiler
d) 32564789
View Answer

Answer: c
Explanation: RAND_MAX is a function used by the compiler to create a maximum random number.
Output:

$ g++ rand1.cpp
$ a.out
2147483647

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

```
    #include <stdio.h>
```
```
    #include <stdlib.h>
```
```
    #include <time.h>
```
```
    int main ()
```
```
    {
```
```
        srand (time(NULL));
```

        printf ("Random number: %d\n", rand() % 100);

```
        srand (1);
```
```
        return 0;
```
```
    }
```

a) 12
b) 23
c) 33
d) Any number from 0 to 99
View Answer

Answer: d
Explanation: This program will create a random number based on time function using srand function.
Output:

$ g++ rand2.cpp
$ a.out
23

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

```
    #include <cstdlib>
```
```
    #include <ctime>
```
```
    #include <iostream>
```
```
    using namespace std;
```
```
    int main()
```
```
    {
```
```
        srand((unsigned)time(0));
```
```
        int ran;
```
```
        for (int i = 0; i < 2; i++)
```
```
        {
```
```
            ran = (rand() % 10) + 1;
```
```
            cout << ran;
```
```
        }
```
```
    }
```

a) 2 4
b) 10 20
c) Any two number from 1 to 10
d) 50 6
View Answer

Answer: c
Explanation: In this program, It will produce two numbers from 1 to 10 by using srand function.
Output:

$ g++ rand3.cpp
$ a.out
4 5

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

```
    #include <iostream>
```
```
    #include <ctime>
```
```
    #include <cstdlib>
```
```
    using namespace std;
```
```
    int main()
```
```
    {
```
```
        srand((unsigned)time(0));
```
```
        int ran;
```
```
        int low = 1, high = 10;
```
```
        int range = (high - low) + 1;
```

        for(int index = 0; index < 1; index++)

```
        {
```

            ran = low + int(range * rand() / (RAND_MAX + 1.0));

```
            cout << ran << endl;
```
```
        }
```
```
    }
```

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

Answer: a
Explanation: In this program the output will always be 1 because as one can observe from the formula used in line #13 that the term inside int() will always be zero. Hence the output will always be 1.
Output: