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This C++ program demonstrates the lexicographical_compare() algorithm. The lexicographical_compare function takes five parameters – the four parameters are begin and end iterators to the two containers and the fifth parameter is a predicate. The predicate we are using is equal_to which is defined in the functional library.

Here is the source code of the C++ program which demonstrates the lexicographical_compare() algorithm. The C++ program is successfully compiled and run on a Linux system. The program output is also shown below.

```
/*
```

 * C++ Program to demonstrate the lexicographical_compare() algorithm

```
 */
```
```
#include <iostream>
```
```
#include <algorithm>
```
```
#include <vector>
```
```
#include <functional>
```
```
 
```
```
void print(const std::vector <int>& v)
```
```
{
```

    std::vector <int>::const_iterator i;

    for(i = v.begin(); i != v.end(); i++)

```
    {
```
```
        std::cout << *i << " ";
```
```
    }
```
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    std::cout << std::endl;
```
```
}
```
```
 
```
```
int main()
```
```
{
```
```
    std::vector <int> a(10), b(10);
```
```
    bool result;
```
```
 
```
```
    for (int i = 0; i < 10 ;i++)
```
```
    {
```
```
        a[i] = i + 1;
```
```
        b[i] = i + 1;
```
```
    }
```
```
    std::cout << "a : ";
```
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    print(a);
```
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    std::cout << "b : ";
```
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    print(b);
```

    // Comparing a and b lexicographically

    result = std::lexicographical_compare(a.begin(), a.end(), b.begin(), b.end(), std::equal_to <int>());

```
    if(result == true)
```
```
    {
```

        std::cout << "a is lexicographically equal to b."

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                  << std::endl;
```
```
    }
```
```
    else
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```
    {
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        std::cout << "a is lexicographically not equal to b."

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

$ a.out
a : 1 2 3 4 5 6 7 8 9 10 
b : 1 2 3 4 5 6 7 8 9 10 
a is lexicographically equal to b.

lexicographical_compare() in C++