Get first and last elements from Array and Vector in CPP

Given an array, find first and last elements of it.

Input: {4, 5, 7, 13, 25, 65, 98}
Output: First element: 4
Last element: 98

In C++, we can use sizeof operator to find number of elements in an array.

// C++ Program to print first and last element in an array 
#include <iostream> 
using namespace std; 
int main() 
{ 
    int arr[] = { 4, 5, 7, 13, 25, 65, 98 }; 
    int f, l, n; 
    n = sizeof(arr) / sizeof(arr[0]); 
    f = arr[0]; 
    l = arr[n - 1]; 
    cout << "First element: " << f << endl; 
    cout << "Last element: " << l << endl; 
    return 0; 
} 

Output:

First element: 4
Last element: 98

We should not sizeof when arrays are passed as parameters, there we must pass size and use that size to find first and last elements.

// C++ Program to print first and last element in an array 
#include <iostream> 
using namespace std; 
  
int printFirstLast(int arr[], int n) 
{ 
    int f = arr[0]; 
    int l = arr[n - 1]; 
    cout << "First element: " << f << endl; 
    cout << "Last element: " << l << endl; 
} 
  
int main() 
{ 
    int arr[] = { 4, 5, 7, 13, 25, 65, 98 }; 
    int n = sizeof(arr) / sizeof(arr[0]); 
    printFirstLast(arr, n); 
    return 0; 
} 

Output:

First element: 4
Last element: 98

In case of vectors in C++, there are functions like front and back to find first and last elements.

// C++ Program to find first and last elements in vector 
#include <iostream> 
#include <vector> 
using namespace std; 
int main() 
{ 
    vector<int> v; 
  
    v.push_back(4); 
    v.push_back(5); 
    v.push_back(7); 
    v.push_back(13); 
    v.push_back(25); 
    v.push_back(65); 
    v.push_back(98); 
    cout << "v.front() is now " << v.front() << '\n'; 
    cout << "v.back() is now " << v.back() << '\n'; 
    return 0; 
} 

Output:

v.front() is now 4
v.back() is now 98

We can use front and back even when vector is passed as a parameter.

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