Self-test 9:
Scope and separate compilation

  1. What is the output of the following program?

    #include <iostream>
using namespace std;

int Number; //global variable

void Increment(int IncNum)
{
        IncNum = IncNum + 3;
        cout << IncNum << endl;
        Number = Number + 1;
}

int main(void)
{
        Number = 1;
        Increment(Number);
        cout << Number << endl;
        return 0;
}
    Solution

    4.
    2

  2. What is the output of the following program?

    #include <iostream>
using namespace std;

int Number; //global variable

void Increment(int& IncNum)
{
        IncNum = IncNum + 3;
        cout << IncNum << endl;
        Number = Number + 1;
}

int main(void)
{
        Number = 1;
        Increment(Number);
        cout << Number << endl;
        return 0;
}
    Solution

    4
    5

  3. What is the output of the following program?

    #include <iostream>
using namespace std;

int Number; //global variable

void Increment(int Number)
{
        Number = Number + 1;
        cout << Number << endl;
}

int main(void) 
{
        Number = 1;
        Increment(Number);
        cout << Number << endl;
        return 0;
}
    Solution

    2
    1

  4. What is the output of the following program?

    #include <iostream>
using namespace std;

int A,B,C,D;

void Two(int A, int B, int& D)
{
        B = 21; D = 23;
        cout << A << " " << B << " " << C << " " << D << endl;
}

void One(int A, int B, int& C)
{
        int D;
        A = 10; B = 11; C = 12; D = 13;
        cout << A << " " << B << " " << C << " " << D << endl;
        Two(A,B,C);
}

int main(void)
{
        A = 1; B = 2; C = 3; D = 4;
        One(A,B,C);
        cout << A << " " << B << " " << C << " " << D << endl;
        Two(A,B,C);
        cout << A << " " << B << " " << C << " " << D << endl;
        return 0;
}
    Solution

    10 11 12 13
    10 21 23 23
    1 2 23 4
    1 21 23 23
    1 2 23 4

  5. Which of the following statements is NOT correct regarding separate compilation?

    1. Repeat the definitions of global constants.
    2. You must add the keyword extern for external variables.
    3. You must add the keyword extern for external functions.
    4. Repeat the function prototypes of external functions.
    Solution

    C. The keyword extern is optional because all C++ functions are global.

  6. Given the definition of the struct

    struct node
{
        int value;
        node left;
        node right;
};

    (a) What is the problem with the above definition? How to fix the bug?

    (b) After fixing the bug, what is the output of the following code:
    sizeof(node);

    Solution

    (a) Here, we have a recursion definition of node, which is not possible in C++. The correct way should be as follow:

    struct node
{
        int value;
        node *left; // pointer to the left node
        node *right; // pointer to the right node 
};

    (b) 12 bytes (in 32-bit machine) and 20 bytes (in 64-bit machines). sizeof computes number of bytes in a struct. In 32-bit machine, each address uses 4 bytes. In 64-bit machine (e.g. in our lab's linux machines), each address uses 8 bytes. So, sizeof(node) = sizeof(int) + 2*sizeof(node*). And, in a 32-bit machine, it is equal to 4 + 4*2 = 12 bytes; in a 64-bit machine, it is equal to 4 + 8*2 = 20 bytes.