# Finding Floor and Ceil of a Sorted Array using C++ STL

In this tutorial, we will be discussing a program to find the floor and ceil of a sorted array using C++ STL.

To find the floor and ceil of a sorted array we will use lower_bound() and upper_bound() functions from STL respectively.

## Example

Live Demo

#include <bits/stdc++.h>
using namespace std;
//finding floor of given array
void printFloor(int arr[], int n1,
int findFloor[], int n2){
int low;
cout << "Floor : ";
for (int i = 0; i < n2; i++) {
low = (lower_bound(arr, arr + n1, findFloor[i]) - arr);
if (arr[low] > findFloor[i])
cout << arr[low - 1] << " ";
else
cout << arr[low] << " ";
}
cout << endl;
}
//fincding ceil of given array
void printCeil(int arr[], int n1,
int findCeil[], int n2){
int up;
cout << "Ceil : ";
for (int i = 0; i < n2; i++) {
up = (upper_bound(arr, arr + n1, findCeil[i]) - arr);
if (arr[up] > findCeil[i] && arr[up - 1] == findCeil[i]) {
cout << arr[up - 1] << " ";
}
else
cout << arr[up] << " ";
}
cout << endl;
}
int main(){
int arr[] = { 1, 2, 4, 7, 11, 12, 23, 30, 32 };
int n1 = sizeof(arr) / sizeof(arr);
cout << "Original Array: ";
for (unsigned int i = 0; i < n1; i++)
cout << " " << arr[i];
cout << "\n";
int find[] = { 1, 3, 5, 7, 20, 24 };
int n2 = sizeof(find) / sizeof(find);
cout << "Values: ";
for (unsigned int i = 0; i < n2; i++)
cout << find[i] << " ";
cout << "\n";
printFloor(arr, n1, find, n2);
printCeil(arr, n1, find, n2);
return 0;
}

## Output

Original Array: 1 2 4 7 11 12 23 30 32
Values: 1 3 5 7 20 24
Floor : 1 2 4 7 12 23
Ceil : 1 4 7 7 23 30