unary_function Program in C++

This C++ program illustrates unary function object base. The DivisibleByFour inherits from the unary_function object base defined in functional library and is passed as a predicate to the for_each algorithm. The elements of vector which are divisible by four are printed.

Here is the source code of the C++ program illustrates unary function object base. The C++ program is successfully compiled and run on a Linux system. The program output is also shown below.

```
/*
```

 * C++ Program to illustrate unary function objects bases

```
 */
```
```
#include <iostream>
```
```
#include <functional>
```
```
#include <vector>
```
```
#include <algorithm>
```
```
 
```

struct DivisibleByFour : public std::unary_function<int, bool> {

```
    bool operator() (int value)
```
```
    {
```
```
        if ((value % 4) == 0)
```
```
        {
```
```
            std::cout << value << " ";
```
```
            return true;
```
```
        }
```
```
        else
```
```
            return false;
```
```
    }
```
```
};
```
```
 
```
```
int main()
```
```
{
```
```
    DivisibleByFour d;
```
```
    std::vector <int> v(20);
```
```
 
```
```
    for (int i = 0; i < 20; i++)
```
```
        v[i] = i + 1;
```

    std::cout << "Range 1 : 20 " << std::endl;

    std::cout << "Elements divisible by 4 : ";

    std::for_each(v.begin(), v.end(), d);

```
    std::cout << std::endl;
```
```
}
```

$ a.out
Range 1 : 20 
Elements divisible by 4 : 4 8 12 16 20

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