What Is the SetPrecision Function in C++?

The C++ setprecision function is used to format floating-point values. This is an inbuilt function and can be used by importing the iomanip library in a program. By using the setprecision function, we can get the desired precise value of a floating-point or a double value by providing the exact number of decimal places. If an argument n is passed to the setprecision() function, then it will give n significant digits of the number without losing any information.

The setprecision() function is quite useful to prevent loss of information. Let us understand this with the help of an example. Let’s say you have to store the value of pi, which has an infinite number of digits. So, in a 4-bit or an 8-bit memory, some digits will get automatically truncated. This will cause a loss of information. To avoid this, the setprecision() function can be used. For example, setprecision(4) will give 4 significant digits (i.e. 3.142) of the value pi without any loss of information.

Syntax of C++ Setprecision

The syntax of the setprecision() function in C++ is as follows:

setprecision(argument)

Parameter description

Argument: This is the integer type parameter that specifies the number of significant digits needed in a floating-point or double value. A parameter n will set the floating point to exactly n significant digits.
Return Value: This function does not return a value. It only manipulates streams.

Significant Figures and Decimal Places

The C++ setprecision can be used to manipulate a complete floating-point value or just its decimal places. These two cases are discussed below:

Significant Figures

To set the precision in a floating-point, simply provide the number of significant figures (say n) required to the setprecision() function as an argument. The function will format the original value to the same number of significant figures (n in this case).

Syntax to print significant figures

cout << setprecision(n) << float_variable;

Here, argument n is the number of significant figures that need to be displayed as output.

The following example will illustrate how to print significant figures using the C++ setprecision:

#include <iostream>

#include <iomanip>

using namespace std;

int main() {

// initialize a floating-point

float num = 2.71828;

cout << "Original number is: " << num;

cout << "\n";

// print 3 significant figures

cout << "The number with 3 significant figures is: ";

cout << setprecision(3) <<num;

cout << "\n\n";

return 0;

}

Cpp_Setprecision_1.

Decimal Places

The C++ setprecision can also be used to format only the decimal places instead of the whole floating-point or double value. This can be done using the fixed keyword before the setprecision() method. When the fixed keyword is used, the argument in the setprecision() function specifies the number of decimal places to be printed in the output.

Syntax to print a significant number of decimal places

cout << fixed << setprecision(n) << float_variable

Here, argument n is the number of decimal places that need to be displayed as output.

The following example will illustrate how to print significant decimal places using the C++ setprecision and the fixed keyword:

#include <iostream>

#include <iomanip>

using namespace std;

int main() {

// initialize a floating-point

float num = 2.71828;

cout << "Original number is: " << num;

cout << "\n";

// print 3 significant figures

cout << "The number with 3 significant figures is: ";

cout << setprecision(3) <<num << endl;

// print 3 decimal places

cout << "The number with 3 decimal places is: ";

cout << fixed << setprecision(3) << num;

cout << "\n\n";

return 0;

}

Cpp_Setprecision_2

Examples of C++ Setprecision Function

Example 1: Using setprecision() Function

In this example, we are going to understand the setprecision() function in a well-explained manner by applying the setprecision() function to set a double value to different significant values:

#include <iostream>

#include <iomanip>

#include <ios>

using namespace std;

int main ()

{

//Initialising the pi as double

double pi = 3.141592653589793238;

cout<<"Value of pi before setting the precision: "

<<pi<<endl;