Output of C++ Program | Set 4

　　Difficulty Level: Rookie

　　Predict the output of below C++ programs.

　　Question 1

 1 #include<iostream>
 2 using namespace std;
 3
 4 int x = 10;
 5 void fun()
 6 {
 7     int x = 2;
 8     {
 9         int x = 1;
10         cout << ::x << endl;
11     }
12 }
13
14 int main()
15 {
16     fun();
17     return 0;
18 }

　　Output: 10
　　If Scope Resolution Operator is placed before a variable name then the global variable is referenced. So if we remove the following line from the above program then it will fail in compilation.

1 int x = 10;

　　Question 2

 1 #include<iostream>
 2 using namespace std;
 3
 4 class Point
 5 {
 6 private:
 7     int x;
 8     int y;
 9 public:
10     Point(int i, int j);  // Constructor
11 };
12
13 Point::Point(int i = 0, int j = 0)
14 {
15     x = i;
16     y = j;
17     cout << "Constructor called";
18 }
19
20 int main()
21 {
22     Point t1, *t2;
23     return 0;
24 }

　　Output: Constructor called.
　　If we take a closer look at the statement “Point t1, *t2;:” then we can see that only one object is constructed here. t2 is just a pointer variable, not an object.

　　Question 3

 1 #include<iostream>
 2 using namespace std;
 3
 4 class Point
 5 {
 6 private:
 7     int x;
 8     int y;
 9 public:
10     Point(int i = 0, int j = 0);    // Normal Constructor
11     Point(const Point &t);            // Copy Constructor
12 };
13
14 Point::Point(int i, int j)
15 {
16     x = i;
17     y = j;
18     cout << "Normal Constructor called\n";
19 }
20
21 Point::Point(const Point &t)
22 {
23     y = t.y;
24     cout << "Copy Constructor called\n";
25 }
26
27 int main()
28 {
29     Point *t1, *t2;
30     t1 = new Point(10, 15);
31     t2 = new Point(*t1);
32     Point t3 = *t1;
33     Point t4;
34     t4 = t3;        //assignment operator
35     return 0;
36 }

　　Output:
　　Normal Constructor called
　　Copy Constructor called
　　Copy Constructor called
　　Normal Constructor called

　　See following comments for explanation:

1 Point *t1, *t2;             // No constructor call
2 t1 = new Point(10, 15);  // Normal constructor call
3 t2 = new Point(*t1);     // Copy constructor call
4 Point t3 = *t1;             // Copy Constructor call
5 Point t4;                 // Normal Constructor call
6 t4 = t3;                 // Assignment operator call

　　

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　　2013-11-27　　15:16:34