Predict the output of below C++ programs.
Question 1
1 #include<iostream>
2
3 using namespace std;
4
5 class Test
6 {
7 int value;
8 public:
9 Test (int v = 0)
10 {
11 value = v;
12 }
13 int getValue()
14 {
15 return value;
16 }
17 };
18
19 int main()
20 {
21 const Test t;
22 cout << t.getValue();
23 return 0;
24 }
Output: Compiler Error.
A const object cannot call a non-const function.
The above code can be fixed by either making getValue() const or making t non-const. Following is modified program with getValue() as const, it works fine and prints 0.
1 #include<iostream>
2
3 using namespace std;
4
5 class Test
6 {
7 int value;
8 public:
9 Test (int v = 0)
10 {
11 value = v;
12 }
13 int getValue() const
14 {
15 return value;
16 }
17 };
18
19 int main()
20 {
21 const Test t;
22 cout << t.getValue();
23 return 0;
24 }
Question 2
1 #include<iostream>
2 using namespace std;
3
4 class Test
5 {
6 int &t;
7 public:
8 Test (int &x)
9 {
10 t = x;
11 }
12 int getT()
13 {
14 return t;
15 }
16 };
17
18 int main()
19 {
20 int x = 20;
21 Test t1(x);
22 cout << t1.getT() << " ";
23 x = 30;
24 cout << t1.getT() << endl;
25 return 0;
26 }
Output: Compiler Error.
Since t is a reference in Test, it must be initialized using Initializer List.
Following is the modified program. It works and prints “20 30″.
1 #include<iostream>
2
3 using namespace std;
4
5 class Test {
6 int &t;
7 public:
8 Test (int &x):t(x) { }
9 int getT() { return t; }
10 };
11
12 int main() {
13 int x = 20;
14 Test t1(x);
15 cout << t1.getT() << " ";
16 x = 30;
17 cout << t1.getT() << endl;
18 return 0;
19 }
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2013-11-27 15:27:57