Precision of Floating Point Numbers in C++ (floor(), ceil(), trunc(), round() and setprecision()) (original) (raw)

Last Updated : 2 Nov, 2022

The 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. Below are a few libraries and methods which are used to provide precision to floating-point numbers in C++:

1. floor() Method

Floor rounds off the given value to the closest integer which is less than the given value. It is defined in the header file.

CPP `

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

// Driver Code 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;

}

`

Time Complexity: O(1)

Auxiliary Space: O(1)

2. ceil() Method

Ceil rounds off the given value to the closest integer which is more than the given value. It is defined in the header file.

CPP `

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

// Driver Code 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;

}

`

Time Complexity: O(1)

Auxiliary Space: O(1)

3. trunc() Method

Trunc rounds remove digits after the decimal point. It is defined in the header file.

CPP `

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

// Driver Code 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;

}

`

Time Complexity: O(1)

Auxiliary Space: O(1)

4. round()

Rounds gave numbers to the closest integer. It is defined in the header files: and .

CPP `

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

// Driver Code 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;

}

`

Time Complexity: O(1)

Auxiliary Space: O(1)

5. setprecision()

Setprecision when used along with 'fixed' provides precision to floating-point numbers correct to decimal numbers mentioned in the brackets of the setprecision. It is defined in header file .

CPP `

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

// Driver Code 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; return 0; }

`

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

Time Complexity: O(1)

Auxiliary Space: O(1)

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