lower_bound() Algorithm in C++

This C++ program demonstrates first occurence of an element using lower_bound algorithm. The program takes an element from the input and the is passed to the lower_bound() function alongwith the iterators to the beginning and end of the vector. The function returns an iterator to the first occurence of the element.

Here is the source code of the C++ program which demonstrates first occurence of an element using lower_bound algorithm. The C++ program is successfully compiled and run on a Linux system. The program output is also shown below.

```
/*
```

 * C++ Program to determine first cccurance of an element using lower_bound() algorithm

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

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

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

```
    {
```
```
        std::cout << *i << " ";
```
```
    }
```
```
    std::cout << std::endl;
```
```
}
```
```
 
```
```
int main()
```
```
{
```

    int arr[] = {1, 2, 2, 2, 3, 3, 5, 6, 7, 7, 8, 9};

    std::vector <int> v(arr, arr + sizeof(arr) / sizeof(int));

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

```
    int find;
```
```
 
```
```
    std::cout << "Vector : ";
```
```
    print(v);
```
```
    std::cout << "Enter the element ";
```
```
    std::cin >> find;
```

    it = lower_bound(v.begin(), v.end(), find);

```
    if(it != v.end())
```
```
    {    
```

        std::cout << "\nFirst position of "<< find << " = "

                  << (it - v.begin()) << std::endl;

```
    }
```
```
    else
```

        std::cout << "Element not found" << std::endl;

```
    return 0;
```
```
}
```

$ a.out
Vector : 1 2 2 2 3 3 5 6 7 7 8 9
Enter the element 7
Last position of 7 = 8

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