C++ Program to Illustrate Const Keyword with Member Functions

This C++ program illustrates the const keyword with member functions. The functions with a const keyword specified before the function definition prevents the calling of non-const data members for a given instance of the class. It also prevents t

Here is the source code of the C++ program which illustrates the const keyword with member functions. The C++ program is successfully compiled and run on a Linux system. The program output is also shown below.

```
/*
```

 * C++ Program to illustrate physical constness

```
 */
```
```
#include <iostream>
```
```
#include <string>
```
```
#include <sstream>
```
```
using namespace std;
```
```
 
```
```
class A {
```
```
    private:
```
```
        int i, j;
```
```
    public:    
```

        A(int ii = 0, int jj = 0) : i(ii), j(jj) {}

        void changeData(int ii, int jj ) {

```
            i = ii;
```
```
            j = jj; 
```
```
        }
```
```
        string getResponse() const {
```
```
            string s;
```
```
            stringstream ss;
```

            ss << "i = " << i << ", j = " << j << "\n";

```
            s = ss.str();
```
```
            return s;
```
```
        }
```
```
        void makeSomeChanges() const;
```
```
 
```
```
};
```
```
 
```
```
/*
```
```
 * Can't change A::i or A::j
```
```
void A::makeSomeChanges() const {
```
```
    i = i + 10;
```
```
    j = j + 10;
```
```
}
```
```
*/
```
```
 
```
```
int main()
```
```
{
```
```
    A a(10, 20);
```
```
 
```

    cout << "A a(10, 20)           : " << a.getResponse();

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    a.changeData(30, 40);
```

    cout << "A::changeData(30, 40) : " << a.getResponse();

```
    // a.makeSomeChanges();
```

    cout << "A::makeSomeChanges()  : " << a.getResponse();

```
}
```

$ a.out
A a(10, 20)           : i = 10, j = 20
A::changeData(30, 40) : i = 30, j = 40
A::makeSomeChanges()  : i = 30, j = 40

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