Precision of floating point numbers in C++ (floor(), ceil(), trunc(), round() and setprecision())

2.5

Decimal equivalent of 1/3 is 0.33333333333333…. An infinite length number would require infinite memory to store, and we typically have 4 or 8 bytes. Therefore, Floating point numbers store only a certain number of significant digits, and the rest are lost. The precision of a floating point number defines how many significant digits it can represent without information loss. When outputting floating point numbers, cout has a default precision of 6 and it truncates anything after that.

Given below are few libraries and methods which are used to provide precision to floating point numbers in C++:

floor():

Floor rounds off the given value to the closest integer which is less than the given value.

// C++ program to demonstrate working of floor()
// in C/C++
#include<bits/stdc++.h>
using namespace std;

int main()
{
    double x =1.411, y =1.500, z =1.711;
    cout << floor(x) << endl;
    cout << floor(y) << endl;
    cout << floor(z) << endl;

    double a =-1.411, b =-1.500, c =-1.611;
    cout << floor(a) << endl;
    cout << floor(b) << endl;
    cout << floor(c) << endl;
    return 0;
}

Output:

1
1
1
-2
-2
-2

ceil():

Ceil rounds off the given value to the closest integer which is more than the given value.

// C++ program to demonstrate working of ceil()
// in C/C++
#include<bits/stdc++.h>
using namespace std;

int main()
{
    double x = 1.411, y = 1.500, z = 1.611;
    cout << ceil(x) << endl;
    cout << ceil(y) << endl;
    cout << ceil(z) << endl;

    double a = -1.411, b = -1.500, c = -1.611;
    cout << ceil(a) << endl;
    cout << ceil(b) << endl;
    cout << ceil(c) << endl;
    return 0;
}

Output:

2
2
2
-1
-1
-1

 

trunc(): 

Trunc rounds removes digits after decimal point.

// C++ program to demonstrate working of trunc()
// in C/C++
#include<bits/stdc++.h>
using namespace std;

int main()
{
    double x = 1.411, y = 1.500, z = 1.611;
    cout << trunc(x) << endl;
    cout << trunc(y) << endl;
    cout << trunc(z) <<endl;

    double a = -1.411, b = -1.500, c = -1.611;
    cout << trunc(a) <<endl;
    cout << trunc(b) <<endl;
    cout << trunc(c) <<endl;
    return 0;
}

Output:

1
1
1
-1
-1
-1

round(): 

Rounds given number to the closest integer.

// C++ program to demonstrate working of round()
// in C/C++
#include<bits/stdc++.h>
using namespace std;

int main()
{
    double x = 1.411, y = 1.500, z = 1.611;

    cout << round(x) << endl;
    cout << round(y) << endl;
    cout << round(z) << endl;

    double a = -1.411, b = -1.500, c = -1.611;
    cout << round(a) << endl;
    cout << round(b) << endl;
    cout << round(c) << endl;
    return 0;
}

Output:

1
2
2
-1
-2
-2

 

setprecision(): 

Setprecision when used along with ‘fixed’ provides precision to floating point numbers correct to decimal numbers mentioned in the brackets of the setprecison.

// C++ program to demonstrate working of setprecision()
// in C/C++
#include<bits/stdc++.h>
using namespace std;

int main()
{
    double pi = 3.14159, npi = -3.14159;
    cout << fixed << setprecision(0) << pi <<" "<<npi<<endl;
    cout << fixed << setprecision(1) << pi <<" "<<npi<<endl;
    cout << fixed << setprecision(2) << pi <<" "<<npi<<endl;
    cout << fixed << setprecision(3) << pi <<" "<<npi<<endl;
    cout << fixed << setprecision(4) << pi <<" "<<npi<<endl;
    cout << fixed << setprecision(5) << pi <<" "<<npi<<endl;
    cout << fixed << setprecision(6) << pi <<" "<<npi<<endl;
}

Output:

3 -3
3.1 -3.1
3.14 -3.14
3.142 -3.142
3.1416 -3.1416
3.14159 -3.14159
3.141590 -3.141590

Note: When the value mentioned in the setprecision() exceeds the number of floating point digits in the original number then 0 is appended to floating point digit to match the precision mentioned by the user.

There exists other methods too to provide precision to floating point numbers. The above mentioned are few of the most commonly used methods to provide precision to floating point numbers during competitive coding.

This article is contributed by Aditya Gupta. If you like GeeksforGeeks and would like to contribute, you can also write an article using contribute.geeksforgeeks.org or mail your article to contribute@geeksforgeeks.org. See your article appearing on the GeeksforGeeks main page and help other Geeks.

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