Ceil and Floor functions in C++

In mathematics and computer science, the floor() and ceil() functions that are defined in <cmath> header file, map a real number to the greatest preceding or the least succeeding integer, respectively.

C++ floor() Function

The floor() function returns the largest integer that is smaller than or equal to the value passed as the argument (i.e.: rounds down the nearest integer).

floor() Syntax

double floor(double x);

Here x is the floating point value. It returns the largest integer smaller than or equal to x.

Example of the floor of some floating point values:

Input : 2.5
Output : 2

Input : -2.1
Output : -3

Example

CPP

// C++ program to demonstrate floor function
#include <iostream>
#include <cmath>
using namespace std;

// Driver function
int main()
{
    // using floor function which return
    // floor of input value
    cout << "Floor of 2.3 is : " << floor(2.3) << endl;
    cout << "Floor of -2.3 is : " << floor(-2.3) << endl;

    return 0;
}

Output

Floor of 2.3 is : 2
Floor of -2.3 is : -3

C++ ceil() Function

ceil() function in C++ returns the smallest integer that is greater than or equal to the value passed as the argument (i.e.: rounds up the nearest integer).

Syntax of ceil()

double ceil(double x);

Here x is the floating point value. It returns the smallest integer greater than or equal to x.

Example of ceil of some floating point values:

Input : 2.5
Output : 3

Input : -2.1
Output : -2

Example

C++

// C++ program to demonstrate ceil function
#include <cmath>
#include <iostream>
using namespace std;

// Driver function
int main()
{
    // using ceil function which return
    // floor of input value
    cout << " Ceil of 2.3 is : " << ceil(2.3) << endl;
    cout << " Ceil of -2.3 is : " << ceil(-2.3) << endl;

    return 0;
}

Output

 Ceil of 2.3 is : 3
 Ceil of -2.3 is : -2

Time Complexity: O(1)
Auxiliary Space: O(1)

Difference between ceil() and floor() in C++

Let us see the differences between ceil() and floor() functions in tabular form:

S.No	ceil() Function	floor() Function
1.	It is used to return the smallest integral value n that is not less than n.	It is used to return the largest integral value n that is not greater than n.
2.	It rounds the n upwards.	It rounds the n downwards.
3.	Its syntax is -: data_type ceil (n);	Its syntax is -: data_type floor (n);